MAX262ACNG-T - Maxim Integrated Products, Inc.

General Description

The MAX260/MAX261/MAX262 CMOS dual second-

order universal switched-capacitor active filters allow

microprocessor control of precise filter functions. No

external components are required for a variety of band-

pass, lowpass, highpass, notch, and allpass configura-

tions. Each device contains two second-order filter

sections that place center frequency, Q, and filter oper-

ating mode under programmed control.

An input clock, along with a 6-bit f0program input,

determine the filter's center or corner frequency without

affecting other filter parameters. The filter Q is also pro-

grammed independently. Separate clock inputs for

each filter section operate with either a crystal, RC net-

work, or external clock generator.

The MAX260 has offset and DC specifications superior

to the MAX261 and MAX262 and a center frequency

(f0) range of 7.5kHz. The MAX261 handles center fre-

quencies to 57kHz, while the MAX262 extends the cen-

ter frequency range to 140kHz by employing lower

clock-to-f0ratios. All devices are available in 24-pin DIP

and small outline packages in commercial, extended,

and military temperature ranges.

Applications

µP-Tuned Filters

Anti-Aliasing Filters

Digital Signal Processing

Adaptive Filters

Signal Analysis

Phase-Locked Loops

Features

♦Filter Design Software Available

♦Microprocessor Interface

♦64-Step Center Frequency Control

♦128-Step Q Control

♦Independent Q and f0Programming

♦Guaranteed Clock to f0Ratio-1% (A grade)

♦75kHz f0Range (MAX262)

♦Single +5V and ±5V Operation

MAX260/MAX261/MAX262

Microprocessor Programmable

Universal Active Filters

________________________________________________________________ Maxim Integrated Products 1

LPA

INB

LPB

BPB

N.C.

HPA

N.C.

BPA

TOP VIEW

OSC OUT

GND

V-

CLK OUT

INA

HPB

A1CLKB

CLKA

V+

MAX260

LPA

INB

LPB

BPB

OP IN

HPA

OP OUT

BPA

HPB

OSC OUT

V-

CLK OUT

INA

GND

A1CLKB

CLKA

V+

MAX261

MAX262

Pin Configurations

Ordering Information

OUTPUT

BPHPLPIN

INPUT

+5V V+

GND

-5V V-

CLKA OSC CLKOUT CLKB

PROGRAM

INPUTS

CRYSTAL

FOURTH-ORDER BANDPASS FILTER

MAX260

MAX261

MAX262

FILTER

Functional Diagram

19-0352; Rev 2; 7/02

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at

1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

PART TEMP RANGE PACKAGE A C C U R A C Y

MAX260ACNG 0°C to +70°C Plastic DIP 1%

MAX260BCNG 0°C to +70°C Plastic DIP 2%

MAX260AENG -40°C to +85°C Plastic DIP 1%

MAX260BENG -40°C to +85°C Plastic DIP 2%

MAX260ACWG 0°C to +70°C Wide SO 1%

MAX260BCWG 0°C to +70°C Wide SO 2%

MAX260AMRG -55°C to +125°C CERDIP 1%

MAX260BMRG -55°C to +125°C CERDIP 2%

*All devices—24-pin packages 0.3in-wide packages

Ordering Information continued at end of data sheet.

MAX260/MAX261/MAX262

Microprocessor Programmable

Universal Active Filters

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional

operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to

absolute maximum rating conditions for extended periods may affect device reliability.

Total Supply Voltage (V+to V-) .............................................15V

Input Voltage, any pin ..........................(V-- 0.3V) to (V++ 0.3V)

Input Current, any pin ......................................................±50mA

Power Dissipation

Plastic DIP (derate 8.33mW/°C above 70°C) ...............660mW

CERDIP (derate 12.5mW/°C above 70°C) .................1000mW

Wide SO (derate 11.8mW/°C above 70°C) ..................944mW

Operating Temperature Ranges

MAX260/MAX261/MAX262XCXG .......................0°C to +70°C

MAX260/MAX261/MAX262XEXG .....................-40°C to +85°C

MAX260/MAX261/MAX262XMXG ..................-55°C to +125°C

Storage Temperature Range .............................-65°C to +160°C

Lead Temperature (Soldering, 10s) ................................+300°C

ELECTRICAL CHARACTERISTICS

(V+= +5V, V-= -5V, CLKA= CLKB= ±5V 350kHz for the MAX260 and 1.5MHz for the MAX261/MAX262, fCLK/f0= 199.49 for

MAX260/MAX261 and 139.80 for MAX262, Filter Mode 1, TA= +25°C, unless otherwise noted.)

PARAMETER CONDITIONS MIN TYP MAX UNITS

f0 Center Frequency Range See Table 1

Maximum Clock Frequency See Table 1

MAX260A ±0.2 ±1.0

MAX260B ±0.2 ±2.0

MAX261/MAX262A ±0.2 ±1.0

fCLK/f0 Ratio Error (Note 1) TA = TMIN to TMAX

MAX261/MAX262B ±0.2 ±2.0

f0 Temperature Coefficient -5 ppm/°C

Q = 8 MAX260A ±1 ±6

Q = 8 MAX260B ±1 ±10

Q = 32 MAX260A ±2 ±10

Q = 32 MAX260B ±2 ±15

Q = 64 MAX260A ±4 ±20

Q = 64 MAX260B ±4 ±25

Q = 8 MAX261/MAX262A ±1 ±6

Q = 8 MAX261/MAX262B ±1 ±10

Q = 32 MAX261/MAX262A ±2 ±10

Q = 32 MAX261/MAX262B ±2 ±15

Q = 64 MAX261/MAX262A ±4 ±20

Q Accuracy (deviation from ideal

continuous filter) (Note 2)

TA = TMIN to

TMAX

Q = 64 MAX261/MAX262B ±4 ±25

Q Temperature Coefficient ±20 ppm/°C

MAX260 ±0.1 ±0.3

DC Lowpass Gain Accuracy MAX261/MAX262 ±0.1 ±0.5 dB

MAX260 -5

MAX261/MAX262 -5

Gain Temperature Coefficient Lowpass (at D.C.)

Bandpass (at f0)MAX260/MAX261/MAX262 +20

ppm/°C

MAX260/MAX261/MAX262

Microprocessor Programmable

Universal Active Filters

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(V+= +5V, V-= -5V, CLKA= CLKB= ±5V 350kHz for the MAX260 and 1.5MHz for the MAX261/MAX262, fCLK/f0= 199.49 for

MAX260/MAX261 and 139.80 for MAX262, Filter Mode 1, TA= +25°C, unless otherwise noted.)

PARAMETER CONDITIONS MIN TYP MAX UNITS

MAX260A ±0.05 ±0.25

MAX260B ±0.15 ±0.45

MAX261A ±0.40 ±1.00

MAX261B ±0.80 ±1.60

MAX262A ±0.40 ±1.20

TA = TMIN to TMAX, Q = 4

Mode 1

MAX262B ±0.80 ±1.60

MAX260A ±0.075 ±0.30

MAX260B ±0.075 ±0.50

MAX261A ±0.50 ±1.10

MAX261B ±0.90 ±1.60

MAX262A ±0.50 ±1.30

Offset Voltage At Filter

Outputs—LP, BP, HP (Note 3)

Mode 3

MAX262B ±0.90 ±1.60

Offset Voltage Temperature

Coefficient

fCLK/f0 = 100.53, Q = 4

TA = TMIN to TMAX ±0.75 mV/°C

Clock Feedthrough ±4 mV

Crosstalk -70 dB

Q = 1, 2nd-Order, LP/BP See Typ. Oper. Char.

4th-Order LP (Figure 26) 90Wideband Noise

4th-Order BP (Figure 24) (Note 4) 100

µVRMS

Harmonic Distortion at f0Q = 4, VIN = 1.5VP-P -67 dB

Supply Voltage Range TA = TMIN to TMAX ±2.37 ±5 ±6.3 V

MAX260 15 20

MAX261 16 20

Power Supply Current (Note 5) TA = TMIN to TMAX

CMOS Level Logic Inputs MAX262 16 20

Shutdown Supply Current Q0A - Q6A = all 0,

CMOS Level Logic Inputs (Note 5) 1.5 mA

INTERNAL AMPLIFIERS

Output Signal Swing TA = TMIN to TMAX, 10kΩ load (Note 6) ±4.75 V

Source 50

Output Signal Circuit Current Sink 2 mA

Power Supply Rejection Ratio 0Hz to 10kHz -70 dB

Gain Bandwidth Product 2.5 MHz

Slew Rate 6V/

MAX260/MAX261/MAX262

Microprocessor Programmable

Universal Active Filters

4 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS (for V± = ±2.5V ±5%)

(V+= +2.37V, V-= -2.37V, CLKA= CLKB= ±2.5V 250kHz for the MAX260 and 1MHz for the MAX261/MAX262, fCLK/f0= 199.49 for

MAX260/MAX261 and 139.80 for MAX262, Filter Mode 1, TA= +25°C, unless otherwise noted.)

PARAMETER CONDITIONS MIN TYP MAX UNITS

f0 Center Frequency Range (Note 7)

Maximum Clock Frequency (Note 7)

MAX26XA ±0.1 1

fCLK/f0 Ratio Error

(Notes 1, 8) Q = 8 MAX26XB ±0.1 2 %

MAX260A ±2 ±6

Q = 8

fCLK/f0 = 199.49 MAX260B ±2 ±10

MAX261A ±2 ±6

fCLK/f0 = 199.49 MAX261B ±2 ±10

MAX262A ±2 ±6

Q Accuracy (deviation from ideal

continuous filter)

(Notes 2, 8)

fCLK/f0 = 139.80 MAX262B ±2 ±10

Output Signal Swing All Outputs (Note 6) ±2 V

Power Supply Current CMOS Level Logic Inputs (Note 5) 7 mA

Shutdown Current CMOS Level Logic Inputs (Note 5) 0.35 mA

Note 1: fCLK/f0accuracy is tested at 199.49 on the MAX260/MAX261, and at 139.8 on the MAX262.

Note 2: Q accuracy tested at Q = 8, 32, and 64. Q of 32 and 64 tested at 1/2 stated clock frequency.

Note 3: The offset voltage is specified for the entire filter. Offset is virtually independent of Q and fCLK/f0ratio setting. The test clock

frequency for mode 3 is 175kHz for the MAX260 and 750kHz for the MAX261/MAX262.

Note 4: Output noise is measured with an RC output smoothing filter at 4 ✕ f0to remove clock feedthrough.

Note 5: TTL logic levels are: HIGH = 2.4V, LOW = 0.8V. CMOS logic levels are: HIGH = 5V, LOW = 0V. Power supply current is typi-

cally 4mA higher with TTL logic and clock input levels.

Note 6: On the MAX260 only, the HP output signal swing is typically 0.75V less than the LP or BP outputs.

Note 7: At ±2.5V supplies, the f0range and maximum clock frequency are typically 75% of values listed in Table 1.

Note 8: fCLK/f0and Q accuracy are a function of the accuracy of internal capacitor ratios. No increase in error is expected at ±2.5V

as compared to ±5V; however, these parameters are only tested to the extent indicated by the MIN or MAX limits.

INTERFACE SPECIFICATIONS (Note 9)

(V+= +5V, V+= -5V, TA= +25°C, unless otherwise noted.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

WR Pulse Width tWR 250 150 ns

Address Setup tAS 25 ns

Address Hold tAH 0ns

Data Setup tDS 100 50 ns

Data Hold tDH 10 0 ns

Logic Input High VIH

WR, D0, D1, A0–A3, CLKA, CLKB

TA =TMIN to TMAX 2.4 V

Logic Input Low VIL

WR, D0, D1, A0–A3, CLKA, CLKB

TA =TMIN to TMAX 0.8 V

Input Leakage Current IIN

WR, D0, D1, A0–A3, CLKB

CLKA

TA =TMIN to TMAX

6µA

Input Capacitance CIN WR, D0, D1, A0–A3, CLKA, CLKB15 pF

Note 9: Interface timing specifications are guaranteed by design and are not subject to test.

MAX260/MAX261/MAX262

Microprocessor Programmable

Universal Active Filters

_______________________________________________________________________________________ 5

Pin Description

MAX260 MAX261/

MAX262

NAME FUNCTION

99V

+Positive supply voltage

17 16 V-Negative supply voltage

18 17 GND

Analog Ground. Connect

to the system ground for

dual supply operation or

mid-supply for single sup-

ply operation. GND should

be well bypassed in single

supply applications.

11 11 CLKA

Input to the oscillator and

clock input to section A.

This clock is internally

divided by 2.

12 12 CLKB

Clock input to filter B. This

clock is internally divided

by 2.

8 8 CLK OUT C l ock outp ut for cr ystal

and R- C osci l l ator op er ati on

19 18 OSC OUT Connects to crystal or R-C

for self-clocked operation

MAX260 MAX261/

MAX262

NAME FUNCTION

5, 23 5, 23 INA, INBFilter inputs

1, 21 1, 21 BPA, BPBBandpass outputs

24, 22 24, 22 LPA, LPBLowpass outputs

3, 14 3, 20 HPA, HPBHighpass/notch/allpass

outputs

16 15 WR Write enable input

15, 13,

10, 7

14, 13,

10, 7

A0, A1,

A2, A3

Address inputs for f0 and

Q input data locations

20, 6 19, 6 D0, D1 Data inputs for f0 and Q

programming

2 OP OUT

Outp ut of uncom m i tted

op am p on M AX 261/

M AX 262 onl y. P i n 2 i s a no-

connect on the M AX 260.

4 OP IN

Inver ti ng i np ut of uncom -

m i tted op am p on M AX 261/

M AX 262 onl y ( noni nver ti ng

i np ut i s i nter nal l y connected

to g r ound ) . P i n 4 i s a no-

connect on the M AX 260.

MAX260/MAX261/MAX262

Microprocessor Programmable

Universal Active Filters

6 _______________________________________________________________________________________

Typical Operating Characteristics

(TA = +25°C, unless otherwise noted.)

-20

-10

0.2 0.60.4 0.8 1.0 1.2 1.4

Q ERROR vs. CLOCK FREQUENCY

MAX260

MAX260/61/62 toc01

CLOCK FREQUENCY (MHz)

Q ERROR (%)

MODE 4

±5V

25°C

Q = 8

fCLK/f0 → N = 0

MODES 2 & 3

MODE 1

IDD vs. POWER SUPPLY VOLTAGE

MAX260/61/62 toc02

V+ TO V- (V)

IDD (mA)

5896 7 10 11 12

CLK FREQ = 500KHz

25°C

CONTROL PINS (5V, 0V)

CLOCKS (5V, 0V)

CLOCKS (5V, -5V)

0.5 1.5 2.5 3.5

IDD vs. CLOCK FREQUENCY

MAX260/61/62 toc03

CLOCK FREQUENCY (MHz)

IDD (mA)

CLOCK (2.4V, 0.8V)

CLOCK (5V, 0V)

±5V

CONTROL PINS (5V, 0V)

25°C

CLOCK (5V, -5V)

-4

0.5 1.51.0 2.0 2.5 3.0 3.5

Q ERROR vs. CLOCK FREQUENCY

MAX261/MAX262

MAX260/61/62 toc04

CLOCK FREQUENCY (MHz)

Q ERROR (%)

MODE 3

MODE 2

MODES 1, 4

±5V

Q = 8

TA = 25°C

→ N = 0

fCLK

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.2

1.0 1.5 2.0 2.5 3.0 3.5

FCLK/F0 ERROR vs. CLOCK FREQUENCY

MAX261/MAX262

MAX260/61/62 toc05

CLOCK FREQUENCY (MHz)

FCLK/F0 ERROR (%)

MODES 2, 3

MODES 1, 4

±5V

Q = 8

TA = 25°C

fCLK

→ N = 0

0.2 1.00.6 1.4 1.8 2.2 2.8 3.0

OUTPUT SIGNAL SWING

vs. CLOCK FREQUENCY

MAX260/61/62 toc06

CLOCK FREQUENCY (MHz)

PEAK TO PEAK, OUTPUT SWING (V)

MAX261/MAX262 ALL MODES

MAX260 MODE 4

±5V

25°C

Q = 8

fCLK/f0→ N = 0

MAX260 MODES 1, 2, 3

Q = 1 Q = 8 Q = 64

MODE LP BP HP/AP/N LP BP HP/AP/N LP BP HP/AP/N

1 -84 -90 -84 -80 -82 -85 -72 -73 -85

2 -88 -90 -88 -84 -82 -84 -77 -73 -76

3 -84 -90 -88 -80 -82 -82 -73 -73 -74

MAX261/

MAX262

4 -83 -89 -84 -79 -81 -85 -71 -73 -85

1 -87 -89 -86 -81 -81 -86 -73 -73 -86

2 -89 -88 -85 -83 -80 -82 -75 -72 -74

3 -87 -88 -85 -80 -82 -80 -71 -72 -72

MAX260

4 -87 -88 -86 -81 -81 -86 -71 -72 -86

MEASUREMENT

BANDWIDTH Q = 1 Q = 8 Q = 64

Wideband -84 -80 -72

3kHz -87 -87 -86

C Message

Weighted -93 -93 -93

Wideband RMS Noise (db ref. to 2.47VRMS, 7VP-P)±5V Supplies

Note 1: fCLK = 1MHz for MAX261/MAX262, fCLK = 350kHz for MAX260

Note 2: fCLK/f0ratio programmed at N = 63 (see Table 2)

Note 3: Clock feedthrough is removed with an RC lowpass ar 4f0, ie., R = 3.9kΩ,

C = 2000pF for MAX261.

Noise Spectral Distribution

(MAX261, fCLK = 1MHz, dB ref. to 2.47VRMS,

7VP-P)

MAX260/MAX261/MAX262

Microprocessor Programmable

Universal Active Filters

_______________________________________________________________________________________ 7

Introduction

Each MAX260/MAX261/MAX262 contains two second-

order switched-capacitor active filters. Figure 1 shows

the filter's state variable topology, employed with two

cascaded integrators and one summing amplifier. The

MAX261 and MAX262 also contain an uncommitted

amplifier. On-chip switches and capacitors provide

feedback to-control each filter section's f0and Q.

Internal capacitor ratios are primarily responsible for

the accuracy of these parameters. Although these

switched-capacitor networks (SCN) are in fact sampled

systems, their behavior very closely matches that of

continuous filters, such as RC active filters. The ratio of

the clock frequency to the filter center frequency

(fCLK/f0) is kept large so that ideal second-order state-

variable response is maintained.

The MAX262 uses a lower range of sampling (fCLK/f0)

ratios than the MAX260 or MAX261 to allow higher

operating f0frequencies and signal bandwidths. These

reduced sample rates result in somewhat more devia-

tion from ideal continuous filter parameters than with

the MAX260/MAX261. However, these differences can

be compensated using Figure 20 (see Application

Hints) or Maxim's filter design software.

The MAX260 employs auto-zero circuitry not included

in the MAX261 or MAX262. This provides improved DC

characteristics, and improved low-frequency perform-

ance at the expense of high-end f0and signal band-

width. The N/HP/AP outputs of the MAX260 are internal-

ly sample-and-held as a result of its auto-zero

operation. Signal swing at this output is somewhat

reduced as a result (MAX260 only). See Table 1 for

bandwidth comparisons of the three filters.

Maxim also provides design programs that aid in con-

verting filter response specifications into the f0and Q

program codes used by the MAX260 series devices.

This software also precompensates f0and Q when low

sample rates are used.

It is important to note that, in all MAX260 series filters,

the filter's internal sample rate is one half the input

clock rate (CLKAor CLKB) due to an internal division

by two. All clock-related data, tables, and other dis-

cussions in this data sheet refer to the frequency at the

CLKAor CLKBinput, i.e., twice the internal sample rate,

unless specifically stated otherwise.

Quick Look Design Procedure

The MAX260, MAX261, and MAX262, with Maxim's filter

design software, greatly simplify the design procedures

for many active filters. Most designs can be realized

using a three-step process described in this section. If

the design software is not used, or if the filter complexi-

ty is beyond the scope of this section, refer to the

remainder of this data sheet for more detailed applica-

tions and design information.

M1M0

SCNIN

S3S1

MODE

SELECT

SCN

Q0–Q6

(TABLE 3)

F0–F5

(TABLE 2)

SAMPLE-HOLD

MAX260 ONLY

N/HP/AP

SCN = SWITCH-CAPACITOR NETWORK

-∫ ∫

SCN

S-H

Figure 1. Filter Block Diagram (One Second-Order Section)

MAX260/MAX261/MAX262

Microprocessor Programmable

Universal Active Filters

8 _______________________________________________________________________________________

Step 1—Filter Design

Start with the program “PZ” to determine what type of

filter is needed. This helps determine the type

(Butterworth, Chebyshev, etc.) and the number of poles

for the optimum choice. The program also plots the fre-

quency response and calculates the pole/zero (f0) and

Q values for each second-order section. Each

MAX260/MAX261/MAX262 contains two second-order

sections, and devices can be cascaded for higher

order filters.

MAX260

MAX261*

MAX262*

INA

OUT

IN 5

(20)14

LPA

HPA

BPA

LPB

HPB

BPB

INB

CLKA

CLKB

16(15)

20(19)

DB-25 MALE PLUG

(BACK VIEW)

15(14)

9 18(17) 17(16) CLK IN

TTL

(SEE FIGURE 4)

0.1µF 0.1µF

-5V+5V

V+V-

GND

*PIN NUMBERS IN ( ) ARE FOR MAX261/MAX262

100 AB$ = "FILTER A" : GOSUB 150 : REM GET DATA FOR SECTION A

110 ADD = 0 : GOSUB 220 : REM WRITE DATA TO THE PRINTER PORT

120 AB$ = "FILTER B" : GOSUB 150 : REM GET DATA FOR B

130 ADD = 32 : GOSUB 220 : REM WRITE DATA TO PRINTER PORT

140 GOTO 100

150 PRINT "MODE (1 to 4, see Table 5) "; AB$; : INPUT M

160 IF M<1 OR M>4 THEN GOTO 150

170 PRINT "CLOCK RATIO (0 to 63, N of Table 2) "; AB$; : INPUT F

180 IF F<0 OR F>63 THEN GOTO 170

190 PRINT "Q (0 to 127, N of Table 3) "; AB$; : INPUT Q

200 IF Q<0 OR Q>127 THEN GOTO 190 ELSE : PRINT

210 RETURN

220 LPRINT CHR$(ADD+M-1); : ADD = ADD+4

230 FOR I = 1 TO 3

240 X = (ADD + (F - 4*INT(F/4))) : LPRINT CHR$(X);

250 F=INT(F/4) : ADD = ADD + 4

260 NEXT I

270 FOR I = 1 TO 4

280 X=(ADD + (Q - 4*INT(Q/4))) : LPRINT CHR$(X);

290 Q=I (Q/4) :: ADD = ADD + 4

300 NEXT I

310 RETURN

Figure 2. Basic Program and Hardware Connections to Parallel Printer Port for “Quick Look” Using a PC

MAX260/MAX261/MAX262

Microprocessor Programmable

Universal Active Filters

_______________________________________________________________________________________ 9

Step 2—Generate Programming

Coefficients

Starting with the f0and Q values obtained in Step 1, use

the program “MPP” to generate the digital coefficients

that program each second-order section's f0and Q. The

program displays values for “N” (“N = _ for f0” and “N =

_ for Q”). N is the decimal equivalent of the binary code

that sets the filter section’s f0or Q. These are the same

“N”s that are listed in Tables 2 and 3.

An input clock frequency and filter mode must also be

selected in this step; however, if a specific-clock rate is

not selected, “GEN” picks one. With regard to mode

selection, mode 1 is the most convenient choice for

most bandpass and lowpass filters. Exceptions are

elliptic bandpass and lowpass filters, which require

mode 3. Highpass filters also use mode 3, while allpass

filters use mode 4. For further information regarding

these filter modes, see the Filter Operating Modes sec-

tion.

Step 3—Loading the Filter

When the N values for the f0and Q of each second-

order filter section are determined, the filter can then be

programmed and operated. What follows is a con-

venient method of programming the filter and evalu-

ating a design if a PC is available.

A short BASIC program loads data into the MAX260/

MAX261/MAX262 through the PC's parallel printer port.

The program asks for the filter mode, as well as the N

values for the f0and Q of each section. These coeffi-

cients are then loaded into the filter in the form of ASCII

characters. This program can be used with or without

Maxim's other filter design software. The program and

the appropriate hardware connections for a Centronics-

type printer port are shown in Figure 2.

Filter Design Software

Maxim provides software programs to help speed the

transition from frequency response design require-

ments to working hardware. A series of programs are

available, including:

Program PZ. Given the requirements, such as center

frequency, Q, passband ripple, and stopband attenua-

tion, PZ calculates the pole frequencies, Q's, zeros,

and the number of stages needed.

Program MPP. For programmed filters, MPP computes

the input codes to use and describes the expected

performance of the design.

Program FR. When a design of one or more stages is

completed, FR checks the final cascaded assembly.

The output frequency response can be compared with

that expected from PZ.

Program PR.BAS Allows a MAX260/MAX261/MAX262

to be programmed through a personal computer. The

mode, f0, and Q of each section are typed in, and the

proper codes are sent to the filter through the comput-

er’s parallel printer port. This program is also provided

in Figure 2.

Other design programs are also included for use with

other Maxim filter products.

Other Filter Products

Maxim has developed a number of other filter products

in addition to the MAX260, MAX261, and MAX262.

PIN-PROGRAMMABLE ACTIVE FILTERS—A dual sec-

ond-order universal filter that needs no external compo-

nents. A microprocessor interface is not required.

MAX263 0.4Hz to 30kHz f0range

MAX264 1Hz to 75kHz f0range

RESISTOR AND PIN-PROGRAMMABLE FILTERS—A

dual second-order universal filter where f0adjustment

beyond pin-programmable resolution employs external

resistors.

MAX265 0.4Hz to 30kHz f0range. Includes two

uncommitted op amps.

MAX266 1Hz to 75kHz f0range. Includes two un-

committed op amps.

MF10 Industry Standard, Resistor Programmed Only

PIN-PROGRAMMABLE BANDPASS FILTERS—A

dual second-order bandpass that needs no external

components. A microprocessor interface is not

required.

MAX267 0.4Hz to 30kHz f0range

MAX268 1Hz to 75kHz f0range

PROGRAMMABLE ANTI-ALIAS FILTER—A program-

mable dual second-order continuous (not switched)

lowpass filter. No clock noise is generated. Designed

for use as an anti-alias filter in front of, or as a smooth-

ing filter following, any sampled filter or system.

MAX270 1kHz to 25kHz Cutoff Frequency Range

5th-ORDER LOW PASS FILTER—Features zero offset

and drift errors for designs requiring high DC accuracy.

MAX280, LT1062 0.1Hz to 20kHz Cutoff Frequency

Range

MAX260/MAX261/MAX262

Microprocessor Programmable

Universal Active Filters

10 ______________________________________________________________________________________

PART Q MODE fCLK f0

1 1 1Hz–400kHz 0.01Hz–4.0kHz

1 2 1Hz–425kHz 0.01Hz–6.0kHz

1 3 1Hz–500kHz 0.01Hz–5.0kHz

1 4 1Hz–400kHz 0.01Hz–4.0kHz

8 1 1Hz–500kHz 0.01Hz–5.0kHz

8 2 1Hz–700kHz 0.01Hz–10.0kH

8 3 1Hz–700kHz 0.01Hz–5.0kHz

8 4 1Hz–600kHz 0.01Hz–4.0kHz

64 1 1Hz–750kHz 0.01Hz–7.5kHz

90 2 1Hz–500kHz 0.01Hz–7.0kHz

64 3 1Hz–400kHz 0.01Hz–4.0kHz

MAX260

64 4 1Hz–750kHz 0.01Hz–7.5kHz

1 1 40Hz–4.0MHz 0.4Hz–40kHz

1 2 40Hz–4.0MHz 0.5Hz–57kHz

1 3 40Hz–4.0MHz 0.4Hz–40kHz

1 4 40Hz–4.0MHz 0.4Hz–40kHz

8 1 40Hz–2.7MHz 0.4Hz–27kHz

8 2 40Hz–2.1MHz 0.5Hz–30kHz

MAX261

PART Q MODE fCLK f0

8 3 40Hz–1.7MHz 0.4Hz–17kHz

8 4 40Hz–2.7MHz 0.4Hz–27kHz

64 1 40Hz–2.0MHz 0.4Hz–20kHz

90 2 40Hz–1.2MHz 0.4Hz–18kHz

64 3 40Hz–1.2MHz 0.4Hz–12kHz

MAX261

64 4 40Hz–2.0MHz 0.4Hz–20kHz

1 1 40Hz–4.0MHz 1.0Hz–100kHz

1 2 40Hz–4.0MHz 1.4Hz–140kHz

1 3 40Hz–4.0MHz 1.0Hz–100kHz

1 4 40Hz–4.0MHz 1.0Hz–100kHz

8 1 40Hz–2.5MHz 1.0Hz–60kHz

6 2 40Hz–1.4MHz 1.4Hz–50kHz

8 3 40Hz–1.4MHz 1.0Hz–35kHz

8 4 40Hz–2.5MHz 1.0Hz–60kHz

64 1 40Hz–1.5MHz 1.0Hz–37kHz

90 2 40Hz–0.9MHz 1.4Hz–32kHz

64 3 40Hz–0.9MHz 1.0Hz–22kHz

MAX262

64 4 40Hz–1.5MHz 1.0Hz–37kHz

Table 1. Typical Clock and Center Frequency Limits

INALPA

N/HP/APABPA

2 6 7

2 4

A0–A3 WR CLKACLKB

OSC OUT CLK OUT OP OUTOP IND0, D1

MODE

A PROGRAM MEMORY

MODE, f0, Q

INTERFACE

LOGIC

÷2

QCK

INBLPB

N/HP/APBBPB

2 6 7

MODE

B PROGRAM MEMORY

MODE, f0, Q ÷2

V+

QCK

V-

GND

MAX261/MAX262 ONLY

∫∫ ∫∫

Figure 3. MAX260/MAX261/MAX262 Block Diagram

MAX260/MAX261/MAX262

Microprocessor Programmable

Universal Active Filters

______________________________________________________________________________________ 11

fCLK/f0 RATIO

MAX260/MAX261 MAX262 PROGRAM CODE

MODES 1,3,4 MODE 2 MODES 1,3,4 MODE 2 N F5 F4 F3 F2 F1 F0

100.53 71.09 40.84 28.88 0000000

102.10 72.20 42.41 29.99 1000001

103.67 73.31 43.98 31.10 2000010

105.24 74.42 45.55 32.21 3000011

106.81 75.53 47.12 33.32 4000100

108.38 76.64 48.69 34.43 5000101

109.96 77.75 50.27 35.54 6000110

111.53 78.86 51.84 36.65 7000111

113.10 79.97 53.41 37.76 8001000

114.67 81.08 54.98 38.87 9001001

116.24 82.19 56.55 39.99 10 001010

117.81 83.30 58.12 41.10 11 001011

119.38 84.42 59.69 42.21 12 001100

120.95 85.53 61.26 43.32 13 001101

122.52 86.64 62.83 44.43 14 001110

124.09 87.75 64.40 45.54 15 001111

125.66 88.86 65.97 46.65 16 010000

127.23 89.97 67.54 47.76 17 010001

128.81 91.80 69.12 48.87 18 010010

130.38 92.19 70.69 49.98 19 010011

131.95 93.30 72.26 51.10 20 010100

133.52 94.41 73.83 52.20 21 010101

135.08 95.52 75.40 53.31 22 010110

136.66 96.63 76.97 54.43 23 010111

138.23 97.74 78.53 55.54 24 011000

139.80 98.86 80.11 56.65 25 011001

141.37 99.97 81.68 57.76 26 011010

142.94 101.08 83.25 58.87 27 011011

14.4.51 102.89 84.82 59.98 28 011100

146.08 103.30 86.39 61.09 29 011101

147.65 104.41 87.96 62.20 30 011110

149.23 105.52 89.54 63.31 31 011111

150.80 106.63 91.11 64.42 32 100000

152.37 107.74 92.68 65.53 33 100001

153.98 108.85 94.25 66.64 34 100010

155.51 109.96 95.82 67.75 35 100011

157.08 111.07 97.39 68.86 36 100100

158.65 112.18 98.96 69.98 37 100101

160.22 113.29 100.53 71.09 38 100110

161.79 114.41 102.10 72.20 39 100111

163.36 115.52 102.67 73.31 40 101000

164.93 116.63 105.24 74.42 41 101001

166.50 117.74 106.81 75.53 42 101010

168.08 118.85 108.38 76.64 43 101011

169.65 119.96 109.96 77.75 44 101100

171.22 121.07 111.53 78.86 45 101101

Table 2. fCLK/f0Program Selection Table

MAX260/MAX261/MAX262

Microprocessor Programmable

Universal Active Filters

12 ______________________________________________________________________________________

Detailed Description

f0and Q Programming

Figure 3 shows a block diagram of the MAX260. Each

second-order filter section has its own clock input and

independent f0and Q control. The actual center fre-

quency is a function of the filter's clock rate, 6-bit f0

control word (see Table 2), and operating mode. The Q

of each section is also set by a separate programmed

input (see Table 3). This way, each half of a MAX260/

MAX261/MAX262 is tuned independently so that com-

plex filter polynomials can be realized. Equations that

convert program code numbers to fCLK/f0and Q values

are listed in the notes beneath Tables 2 and 3.

Oscillator and Clock Inputs

The clock circuitry of the MAX260/MAX261/MAX262

can operate with a crystal, resistor-capacitor (RC) net-

work, or an external clock generator as shown in Figure

4. If an RC oscillator is used, the clock rate, fCLK, nomi-

nally equals 0.45/RC.

The duty cycle of the clock at CLKAand CLKBis unim-

portant because the input is internally divided by 2 to

generate the sampling clock for each filter section. It is

important to note that this internal division also halves

the sample rate when considering aliasing and other

sampled system phenomenon.

Microprocessor Interface

f0, Q, and mode-selection data are stored in internal

program memory. The memory contents are updated

by writing to addresses selected by A0–A3. D0, and D1

are the data inputs. A map of the memory locations is

shown in Table 4. Data is stored in the selected

address on the rising edge of WR. Address and data

inputs are TTL and CMOS compatible when the filter is

powered from ±5V. With other power supply voltages,

CMOS logic levels should be used. Interface timing is

shown in Figure 5. Note: Clock inputs CLKAand CLKB

have no relation to the digital interface. They control the

switched-capacitor filter sample rate only.

Some noise may be generated on the filter outputs by

transitions at the logic inputs. If this is objectionable,

fCLK/f0 RATIO

MAX260/MAX261 MAX262 PROGRAM CODE

MODES 1,3,4 MODE 2 MODES 1,3,4 MODE 2 N F5 F4 F3 F2 F1 F0

172.79 122.18 113.10 79.97 46 101110

174.36 123.29 114.66 81.08 47 101111

175.93 124.40 11624 82.19 48 110000

177.50 125.51 117.81 83.30 49 110001

179.07 126.62 119.38 84.41 50 110010

180.64 127.73 120.95 85.53 51 110011

182.21 128.84 122.52 86.64 52 110100

183.78 129.96 124.09 87.75 53 110101

185.35 131.07 125.66 88.86 54 110110

186.92 132.18 127.23 89.97 55 110111

188.49 133.29 128.81 91.08 56 111000

190.07 134.40 130.38 92.19 57 111001

191.64 135.51 131.95 93.30 58 111010

193.21 136.62 133.52 94.41 59 111011

194.78 137.73 135.09 95.52 60 111100

196.35 138.84 136.66 96.63 61 111101

197.92 139.95 138.23 97.74 62 111110

199.49 141.06 139.80 98.85 63 111111

Table 2. fCLK/f0Program Selection Table (continued)

Note 1: For the MAX260/MAX261, fCLK/f0= (64 + N)π / 2 in modes 1, 3, and 4, where N varies from 0 to 63.

Note 2: For the MAX262, fCLK/f0= (26 s N)π / 2 in modes 1, 3, and 4, where N varies 0 to 63.

Note 3: In mode 2, all fCLK/f0ratios are divided by √2. The functions are then:

MAX260/MAX261 fCLK/f0= 1.11072 (64 + N), MAX262 fCLK/f0= 1.11072 (26 + N)

MAX260/MAX261/MAX262

Microprocessor Programmable

Universal Active Filters

______________________________________________________________________________________ 13

PROGRAMMED Q PROGRAM CODE

MODES

1,3,4

MODE

2N Q6Q5Q4Q3Q2Q1Q0

0.500* 0.707* 0* 0 0 0 0 0 0 0

0.504 0.713 1 0 0 0 0 0 0 1

0.508 0.718 2 0 0 0 0 0 1 0

0.512 0.724 3 0 0 0 0 0 1 1

0.516 0.730 4 0 0 0 0 1 0 0

0.520 0.736 5 0 0 0 0 1 0 1

0.525 0.742 6 0 0 0 0 1 1 0

0.529 0.748 7 0 0 0 0 1 1 1

0.533 0.754 8 0 0 0 1 0 0 0

0.538 0.761 9 0 0 0 1 0 0 1

0.542 0.767 10 0 0 0 1 0 1 0

0.547 0.774 11 0 0 0 1 0 1 1

0.552 0.780 12 0 0 0 1 1 0 0

0.556 0.787 13 0 0 0 1 1 0 1

0.561 0.794 14 0 0 0 1 1 1 0

0.566 0.801 15 0 0 0 1 1 1 1

0.571 0.808 16 0 0 1 0 0 0 0

0.577 0.815 17 0 0 1 0 0 0 1

0.582 0.823 18 0 0 1 0 0 1 0

0.587 0.830 19 0 0 1 0 0 1 1

0.593 0.838 20 0 0 1 0 1 0 0

0.598 0.646 21 0 0 1 0 1 0 1

0.604 0.854 22 0 0 1 0 1 1 0

0.609 0.862 23 0 0 1 0 1 1 1

PROGRAMMED Q PROGRAM CODE

MODES

1,3,4

MODE

2N Q6Q5Q4Q3Q2Q1Q0

0.615 0.870 24 0 0 1 1 0 0 0

0.621 0.879 25 0 0 1 1 0 0 1

0.627 0.887 26 0 0 1 1 0 1 0

0.634 0.896 27 0 0 1 1 0 1 1

0.640 0.905 28 0 0 1 1 1 0 0

0.646 0.914 29 0 0 1 1 1 0 1

0.653 0.924 30 0 0 1 1 1 1 0

0.660 0.933 3100 11 11 1

0.667 0.943 3201 00 00 0

0.674 0.953 3301 00 00 1

0.681 0.963 3401 00 01 0

0.688 0.973 3501 00 01 1

0.696 0.984 3601 00 10 0

0.703 0.995 3701 00 10 1

0.711 1.01 3801 00 11 0

0.719 1.02 3901 00 11 1

0.727 1.03 4001 01 00 0

0.736 1.04 4101 01 00 1

0.744 1.05 4201 01 01 0

0.753 1.06 43 0 1 0 1 0 1 1

0.762 1.08 44 0 1 0 1 1 0 0

0.771 1.09 45 0 1 0 1 1 0 1

0.780 1.10 46 0 1 0 1 1 1 0

0.790 1.12 47 0 1 0 1 1 1 1

Table 3. Q Program Selection Table

Note 4: * Writing all 0s into Q0A–Q6A on Filter A activates a low-power shutdown mode. BOTH filter sections are deactivated.

Therefore, this Q value is only achievable in filter B.

MAX260/MAX261/MAX262

Microprocessor Programmable

Universal Active Filters

14 ______________________________________________________________________________________

PROGRAMMED Q PROGRAM CODE

MODES

1,3,4

MODE

2N Q6Q5Q4Q3Q2Q1Q0

0.800 1.13 48 0110000

0.810 1.15 49 0110001

0.821 1.16 50 0110010

0.831 1.18 51 0110011

0.842 1.19 52 0110100

0.853 1.21 53 0110101

0.865 1.22 54 0110110

0.877 1.24 55 0110111

0.889 1.26 56 0111000

0.901 1.27 57 0111001

0.914 1.29 58 0111010

0.928 1.31 59 0111011

0.941 1.33 60 0111100

0.955 1.35 61 0111101

0.969 1.37 62 0111110

0.985 1.39 63 0111111

1.00 1.41 64 1000000

1.02 1.44 65 1000001

1.03 1.46 66 1000010

1.05 1.48 67 1000011

1.07 1.51 68 1000100

1.08 1.53 69 1000101

1.10 1.56 70 1000110

1.12 1.59 71 1000111

1.14 1.62 72 1001000

1.16 1.65 73 1001001

1.19 1.68 74 1001010

1.21 1.71 75 1001011

1.23 1.74 76 1001100

1.25 1.77 77 1001101

1.28 1.81 78 1001110

1.31 1.85 79 1001111

1.33 1.89 80 1010000

1.36 1.93 81 1010001

1.39 1.97 82 1010010

1.42 2.01 83 1010011

1.45 2.06 84 1010100

1.49 2.10 85 1010101

1.52 2.16 86 1010110

1.56 2.21 87 1010111

PROGRAMMED Q PROGRAM CODE

MODES

1,3,4

MODE

2N Q6Q5Q4Q3Q2Q1Q0

1.60 2.26 88 1 0 1 1 0 0 0

1.64 2.32 89 1 0 1 1 0 0 1

1.68 2.40 90 1 0 1 1 0 1 0

1.73 2.45 91 1 0 1 1 0 1 1

1.78 2.51 92 1 0 1 1 1 0 0

1.83 2.59 93 1 0 1 1 1 0 1

1.88 2.66 94 1 0 1 1 1 1 0

1.94 2.74 95 1 0 1 1 1 1 1

2.00 2.83 96 1 1 0 0 0 0 0

2.06 2.92 97 1 1 0 0 0 0 1

2.13 3.02 98 1 1 0 0 0 1 0

2.21 3.12 99 1 1 0 0 0 1 1

2.29 3.23 100 1 1 0 0 1 0 0

2.37 3.35 101 1 1 0 0 1 0 1

2.46 3.48 102 1 1 0 0 1 1 0

2.56 3.62 103 1 1 0 0 1 1 1

2.67 3.77 104 1 1 0 1 0 0 0

2.78 3.96 105 1 1 0 1 0 0 1

2.91 4.11 106 1 1 0 1 0 1 0

3.05 4.31 107 1 1 0 1 0 1 1

3.20 4.53 108 1 1 0 1 1 0 0

3.37 4.76 109 1 1 0 1 1 0 1

3.56 5.03 110 1 1 0 1 1 1 0

3.76 5.32 111 1 1 0 1 1 1 1

4.00 5.66 112 1 1 1 0 0 0 0

4.27 6.03 113 1 1 1 0 0 0 1

4.57 6.46 114 1 1 1 0 0 1 0

4.92 6.96 115 1 1 1 0 0 1 1

5.33 7.54 116 1 1 1 0 1 0 0

5.82 8.23 117 1 1 1 0 1 0 1

6.40 9.05 118 1 1 1 0 1 1 0

7.11 10.1 119 1 1 1 0 1 1 1

8.00 11.3 120 1 1 1 1 0 0 0

9.14 12.9 121 1 1 1 1 0 0 1

10.7 15.1 122 1 1 1 1 0 1 0

12.8 18.1 123 1 1 1 1 0 1 1

16.0 22.6 124 1 1 1 1 1 0 0

21.3 30.2 125 1 1 1 1 1 0 1

32.0 45.3 126 1 1 1 1 1 1 0

64.0 90.5 127 1 1 1 1 1 1 1

Table 3. Q Program Selection Table (continued)

Notes 5) In modes 1, 3, and 4: Q = 64 / (128 - N)

6) In mode 2, the listed Q values are those of mode 1 multiplied by √2. Then Q = 90.51 / (128 - N)

MAX260/MAX261/MAX262

Microprocessor Programmable

Universal Active Filters

______________________________________________________________________________________ 15

the digital lines should be buffered from the device by

logic gates as shown in Figure 6.

Shutdown Mode

The MAX260/MAX261/MAX262 enters a shutdown/

standby mode when all zeroes are written to the Q

addresses of filter A (Q0A–Q6A). When shut down,

power consumption with ±5V supplies typically drops

to 10mW. When reactivating the filter after shutdown,

allow 2ms to return to full operation.

Filter Operating Modes

There are several ways in which the summing amplifier

and integrators in each MAX260/MAX261/MAX262 filter

section can be configured. The four most versatile

interconnections (modes) are selected by writing to

inputs M0 and M1 (see Tables 4 and 5). These modes

use no external components. A fifth mode, 3A, makes

use of an additional op amp (included in the MAX261

and MAX262) and external resistors, but uses the same

internal configuration and is selected with the same

programming code, as mode 3.

FILTER B

CLK

OUT

CLKB

fCLK = 0.45

OSC

OUT

19(18)*

CLKA

FILTER A

FILTER B

CLK

OUT CLKB

OSC

OUT

CLKA

FILTER A

19(18)*

CRYSTAL

*OSC OUT IS PIN 18 ON MAX261/MAX262

FILTER B

CLK

OUT

CLKB

OSC

OUT

N.C.

CLKA

FILTER A

N.C.

EXTERNAL CLOCK IN

(ANY DUTY CYCLE)

Figure 4. Clock Input Connections

DATA BIT ADDRESS

D0 D1 A3 A2 A1 A0 LOCATION

FILTER A

M0AM1A0000 0

F0AF1A0001 1

F2AF3A0010 2

F4AF5A0011 3

Q0AQ1A0100 4

Q2AQ3A0101 5

Q4AQ5A0110 6

Q6A0111 7

FILTER B

M0BM1B1000 8

F0BF1B1001 9

F2BF3B1010 10

F4BF5B1011 11

Q0BQ1B1100 12

Q2BQ3B1101 13

Q4BQ5B1110 14

Q6B1111 15

Table 4. Program Address Locations

Note: Writing 0 into Q0A–Q6A (address locations 4–7) on filter

A activates shutdown mode. BOTH filter sections deactivate.

D0, D1

VALID DATA

tDS tDH

tWR

VALID ADDRESS

tAS

A0–A3

SEE INTERFACE SPECIFICATIONS FOR TIMING LIMITS

tAH

Figure 5. Interface Timing

MAX260/MAX261/MAX262

Microprocessor Programmable

Universal Active Filters

16 ______________________________________________________________________________________

Figures 7 through 11 show symbolic representations of

the MAX260 filter modes. Only one second-order sec-

tion is shown in each case. The A and B sections of

one MAX260/MAX261/MAX262 can be programmed for

different modes if desired. The f0, fN(notch), Q, and

various output gains in each case are shown in Table 5.

Filter Mode Selection

MODE 1 (Figure 7) is useful when implementing allpole

lowpass and bandpass filters such as Butterworth,

Chebyshev, Basset, etc. It can also be used for notch

filters, but only second-order notches because the rela-

tive pole and zero locations are fixed. Higher order

notch filters require more latitude in f0and 1N, which is

why they are more easily implemented with mode 3A.

OCTAL D FLIP-FLOP

74HC374

VCC

11011

-5V

OC CKGND

MAX260

MAX261

MAX262

+5V

V+

-5V

V-

GND

Figure 6. Buffering/Latching Logic Inputs

SCN

SCN NBP

MODE 1

-∫ ∫

SCN

SCN = SWITCHED-CAPACITOR NETWORK

Figure 7. Filter Mode 1: Second-Order Bandpass, Lowpass,

and Notch

MODE M1,

FILTER

FUNCTIONS f0Qf

NHOLP HOBP HON1

(f ➝ 0)

HON2

(f ➝ fCLK/4) OTHER

1 0, 0 LP, BP, N f0-1 -Q -1 -1

2 0, 1 LP, BP, N f0√2-0.5 -Q/√2-0.5 -1

3 1, 0 LP, BP, HP -1 -Q HOHP = -1

-1 -Q HOHP = -1

4 1, 1 LP, BP, AP

SEE TABLE 2

SEE TABLE 3

-2 -2Q HOAP = -1

fZ = f0, QZ = Q

Table 5. Filter Modes for Second-Order Functions

Notes: f0= Center Frequency

fN= Notch Frequency

HOLP = Lowpass Gain at DC

HOBP = Bandpass Gain at f0

HOHP = Highpass Gain as f approaches fCLK/4

HON1 = Notch Gain as f approaches DC

HON2 = Notch Gain as f approaches fCLK/4

HOAP = Allpass Gain

fz, Qz= f and Q of Complex Pole Pair

MAX260/MAX261/MAX262

Microprocessor Programmable

Universal Active Filters

______________________________________________________________________________________ 17

Mode 1, along with mode 4, supports the highest clock

frequencies (see Table 1) because the input summing

amplifier is outside the filter’s resonant loop (Figure 7).

The gain of the lowpass and notch outputs is 1, while

the bandpass gain at the center frequency is Q. For

bandpass gains other than Q, the filter input or output

can be scaled by a resistive divider or op amp.

MODE 2 (Figure 8) is used for all-pole lowpass and

bandpass filters. Key advantages compared to mode 1

are higher available Qs (see Table 3) and lower output

noise. Mode 2’s available fCLK/f0ratios are √2less than

with mode 1 (see Table 2), so a wider overall range of

f0s can be selected from a single clock when both

modes are used together. This is demonstrated in the

Wide Passband Chebyshev Bandpass design example.

MODE 3 (Figure 9) is the only mode that produces

high-pass filters. The maximum clock frequency is

somewhat less than with mode 1 (see Table 1).

MODE 3A (Figure 10) uses a separate op amp to sum

the highpass and lowpass outputs of mode 3, creating

a separate notch output. This output allows the notch to

be set independently of f0by adjusting the op amp’s

feedback resistor ratio (RH, RL). RH, RL, and RGare

external resistors. Because the notch can be indepen-

dently set, mode 3A is also useful when designing

pole-zero filters such as elliptics.

MODE 4 (Figure 11) is the only mode that provides an

allpass output. This is useful when implementing group

delay equalization. In addition to this, mode 4 can also

be used in all pole lowpass and bandpass filters. Along

with mode 1, it is the fastest operating mode for the fil-

ter, although the gains are different than in mode 1.

When the allpass function is used, note that some

amplitude peaking occurs (approximately 0.3dB when

Q = 8) at f0. Also note that f0and Q sampling errors are

highest in mode 4 (see Figure 20).

SCN

SCN NBP

MODE 2

-∫ ∫

SCN

Figure 8. Filter Mode 2: Second-Order Bandpass, Lowpass,

and Notch

SCN

SCN HP BP

MODE 3

-∫ ∫

SCN

SCN = SWITCHED-CAPACITOR NETWORK

Figure 9. Filter Mode 3: Second-Order Bandpass, Lowpass,

and Highpass

SCN

SCN HP

MODE 3A

∫ ∫

SCN

SCN = SWITCHED-CAPACITOR NETWORK

Figure 10. Filter Mode 3a: Second-Order Bandpass, Lowpass,

Highpass, and Notch. For elliptic LP, BP, HP, and Notch, the N

output is used.

MAX260/MAX261/MAX262

Microprocessor Programmable

Universal Active Filters

18 ______________________________________________________________________________________

Description of Filter Functions

BANDPASS (Figure 12)

For all pole bandpass and lowpass filters (Butterworth,

Bessel, Chebyshev) use mode 1 if possible. If appropri-

ate fCLK/f0or Q values are not available in mode 1,

mode 2 provides a selection that is closer to the

required values. Mode 1, however, has the highest

bandwidth (see Table 1). For pole-zero filters, such as

elliptics, see mode 3A.

HOBP = Bandpass output gain at ω= ωo

f0= ω0 / 2π= The center frequency of the complex

pole pair. Input-output phase shift is -180°at f0.

Q = The quality factor of the complex pole pair.

Also the ratio of f0to -3dB bandwidth of the

second-order bandpass response.

LOWPASS See bandpass text. (Figure 13)

HOLP = Lowpass output gain at DC

f0= ω0 / 2π

HIGHPASS (Figure 14)

Mode 3 is the only mode with a highpass output. It

works for all pole filter types such as Butterworth,

Bessel and Chebyshev. Use mode 3A for filters

employing both poles and zeros, such as elliptics.

HOHP = Highpass output gain as f approaches fCLK/4

f0= ω0 / 2π

NOTCH (Figure 15)

Mode 3A is recommended for multi-pole notch filters. In

second-order filters, mode 1 can also be used. The

advantages of mode 1 are higher bandwidth, com-

pared to mode 3 (higher fNcan be implemented), and

no need for external components as required in mode

3A.

HON2 = Notch output gain as f approaches fCLK/4

HON1 = Notch output gain as f approaches DC

fn= ωn / 2π

ALLPASS

Mode 4 is the only configuration in which an allpass

function can be realized.

Gs H s

ss Q

ON n

()

( / )

ωω

Gs H s

ss Q

OHP

()

( / )

=++

22ωω

Gs H

ss Q

OLP o

()

( / )

=++

ωω

Gs H sQ

ss Q

OBP o

() ( / )

( / )

=++

ωω

SCN

SCN AP

MODE 4

-∫ ∫

SCN

SCN = SWITCHED-CAPACITOR NETWORK

Figure 11. Filter Mode 4: Second-Order Bandpass, Lowpass,

and Allpass

fLfOfH

HOBP

0.707 HOBP

BANDPASS OUTPUT

f(LOG SCALE)

GAIN (V/V)

Figure 12. Second-Order Bandpass Characteristics

Off

=−

=−+







+





















+













MAX260/MAX261/MAX262

Microprocessor Programmable

Universal Active Filters

______________________________________________________________________________________ 19

HOAP = Allpass output gain for DC < f < fCLK / 4

f0= ω0 / 2π

Filter Design Procedure

The procedure for most filter designs is to first convert

the required frequency response specifications to f0s

and Qs for the appropriate number of second-order

sections that implement the filter. This can be done by

using design equations or tables in available liter-

ature, or can be conveniently calculated using Maxim's

filter design software. Once the f0s and Qs have been

found, the next step is to turn them into the digital pro-

gram coefficients required by the MAX260/MAX261/

MAX262. An operating mode and clock frequency (or

clock/center frequency ratio) must also be selected.

Next, if the sample rate (fCLK/2) is low enough to cause

significant errors, the selected f0s and Qs should be

corrected to account for sampling effects by using

Figure 20 or Maxim's design software. In most cases,

the sampling errors are small enough to require no cor-

rection, i.e., less than 1%. In any case, with or without

correction, the required f0s and Qs can then be select-

ed from Tables 2 and 3. Maxim's filter design software

Gs H ssQ

ss Q

OAP oo

() ( / )

( / )

=−+

ωω

fPfC

HOP

0.707 HOLP

HOLP

LOWPASS OUTPUT

f(LOG SCALE)

GAIN (V/V)

Figure 13. Second-Order Lowpass Characteristics

ffX QQ

fp f Q

HHX

OP OLP

=







+







+

−−

−

211

111

fCfP

HOP

0.707 HOHP

HOHP

HIGHPASS OUTPUT

f(LOG SCALE)

GAIN (V/V)

Figure 14. Second-Order Highpass Characteristics

ffX QQ

fp f Q

HHX

OP OHP

=







+







+













−−

−

211

111

f(LOG SCALE)

GAIN (V/V)

HON1

HON

HON2

Figure 15. Second-Order Notch Characteristics

TOTAL SECTIONS TOTAL B.W. TOTAL Q

1 1.000 B 1.00 Q

2 0.644 B 1.55 Q

3 0.510 B 1.96 Q

4 0.435 B 2.30 Q

5 0.386 B 2.60 Q

Table 6. Cascading Identical Bandpass

Filter Sections

Note: B = individual stage bandwidth, Q = individual

stage Q.

MAX260/MAX261/MAX262

Microprocessor Programmable

Universal Active Filters

20 ______________________________________________________________________________________

can also perform this last step. The desired f0s and Qs

are stated, and the appropriate digital coefficients are

supplied.

Cascading Filters

In some designs, such as very narrow band filters, sev-

eral second-order sections with identical center fre-

quency can be cascaded. The total Q of the resultant

filter is:

Q is the Q of each individual filter section, and N is the

number of sections. In Table 6, the total Q and band-

width are listed for up to five identical second-order

sections. B is the bandwidth of each section.

In high-order bandpass filters, stages with different f0s

and Qs are also often cascaded. When this happens,

the overall filter gain at the bandpass center frequency

is not simply the product of the individual gains

because f0, the frequency where each sections gain is

specified, is different for each second-order section.

The gain of each section at the cascaded filter's center

frequency must be determined to obtain the total gain.

For all-pole filters the gain, H(f0), as each second-order

section's f0is divided by an adjustment factor, G, to

obtain that section's gain, H(f0BP), at the overall center

frequency:

H1(f0BP) = H(f01) / G1= Section 1’s Gain at f0BP

where F1= f01 / fOBP

G1, Q1, and f01 are the gain adjustment factor, Q, and

f0for the first of the cascaded second-order sections.

The gain of the other sections (2, 3, etc.) at f0BP is

determined the same way. The overall gain is:

H(f0Bp) = H1(f0BP) x H2(f0BP) x etc.

For cascaded filters with zeros (fZ) such as elliptics, the

gain adjustment factor for each stage is:

where F1Z = fz1 / f0BP, and F1is the same as above.

Application Hints

Power Supplies

The MAX260/MAX261/MAX262 can be operated with a

variety of power supply configurations, including +5V to

+12V single supply or ±2.5V to ±5V dual supplies.

When a single supply is used, V-is connected to sys-

tem ground and the filter's GND pin should be biased

at V+/2. The input signal is then either capacitively cou-

pled to the filter input or biased to V+/2. Figure 16

shows circuit connections for single-supply operation.

When power supplies other than ±5V are used, CMOS

input logic levels (HIGH = V+, LOW = GND or V-) are

required for WR, D0, D1, A0–A3, OLKA, and CLKB.

With ±5V supplies, either TTL or CMOS levels can be

used. Note, however, that power consumption at ±5V is

reduced if CLKAand CLKBare driven with ±5V, rather

than TTL or 0 to 5V levels. Operation with +5V or ±2.5V

power lowers power consumption, but also reduces

bandwidth by approximately 25% compared to +12V or

±5V supplies.

Best performance is achieved if V+and V-are bypassed

to ground with 4.7µF electrolytic (Tantalum is preferred.)

and 0.1µF ceramic capacitors. These should be located

as close to the supply pins as possible. The lead length

of the bypass capacitors should be shortest at the V+

and V-pins. When using a single supply, V+and GND

should be bypassed to V-as shown in Figure 16.

Output Swing and Clipping

MAX260/MAX261/MAX262 outputs are designed to

drive 10kΩloads. For the MAX261 and MAX262, all fil-

ter outputs swing to within 0.15V of each supply rail

with a 10kΩload. In the MAX260 only, an internal sam-

ple-hold circuit reduces voltage swing at the N/HP/AP

output compared to LP and BR. N/HP/AP, therefore,

swings to within 1V (10kΩload) of either rail on the

MAX260.

To ensure that the outputs are not driven beyond their

maximum range (output clipping), the peak amplitude

response, individual section gains (HOBP, HOLP,

HOHP), input signal level, and filter offset voltages must

be carefully considered. It is especially important to

check unused outputs for clipping (i.e., the lowpass

output in a bandpass hookup), because overload at

any filter stage severely distorts the overall response.

The maximum signal swing with ±4.75V supplies and a

1.0V filter offset is approximately ±3.5V.

For example, lets assume a fourth-order lowpass filter is

being implemented with a Q of 2 using mode 1. With a

single 5V supply (i.e., ±2.5V with respect to chip GND)

the maximum output signal is ±2V (w.r.t. GND). Since in

QF F F F Q

2211

212

( ) ( / )

=−









−+











−







QF F Q

2211

212

( ) ( / ) /

=−+











Total Q Q

−

()

MAX260/MAX261/MAX262

Microprocessor Programmable

Universal Active Filters

______________________________________________________________________________________ 21

mode 1 the maximum signal is 0 times the input signal,

the input should not exceed ±(2/Q)V, or ±1V in this case.

Clock Feedthrough and Noise

Typical wideband noise for MAX260 series devices is

0.5mVP-P from DC to 100kHz. The noise is virtually

independent of clock frequency. In multistage filters,

the section with the highest Q should be placed first for

lower output noise.

The output waveform of the MAX260 series and other

switched capacitor filters appears as a sampled signal

with stepping or “staircasing” of the output waveform

occurring at the internal sample rate (fCLK/2). This step-

ping, if objectionable, can be removed by adding a sin-

gle-pole AC filter. With no input signal, clock-related

feedthrough is approximately 8mVP-P. This can also be

attenuated with an RC-smoothing filter as shown with

the MAX261 in Figure 17.

Some noise also can be generated at the filter outputs

by transitions at the logic inputs. If this is objectionable,

the digital lines should be buffered from the device by

logic gates as shown in Figure 6.

Input Impedance

The input to each filter is the switched capacitor circuit

shown in Figure 18. In the MAX260, the input capacitor

charges to the input voltage VIN during the first half

clock cycle. During the second half-cycle, its charge is

transferred to the feedback capacitor. The resultant

input impedance can be approximated by:

RIN = 1 / (CINfCLK / 2) = 2 / (CINfCLK).

CIN is around 12pF, hence, for a clock frequency of

500kHz, RIN = 333kΩ. The input also has about 5pF of

fixed capacitance to ground.

The MAX261/MAX262 input structure is shown in Figure

19. Here CA= 12pF and CB= 0.016pF and only CBis

switched, so the input resistance is 750 times larger

compared to the MAX260 (RIN = 250MΩ). The

MAX261/MAX262 have a fixed capacitance of approxi-

mately 5pF to ground.

f0and Q at Low Sample Rates

When low fCLK/f0ratios and low Q settings are select-

ed, deviation from ideal continuous filter response can

be noticeable in some designs. This is due to interac-

tion between Q and f0at low fCLK/f0ratios and Qs. The

data in Figure 20 quantifies these differences. Since the

MAX260

MAX261

MAX262

A0–A3

D0, D1

INA

INB

CMOS

LOGIC

LEVELS

V+

V-

GND

0.1µF0.1µF

+5V

4.7µF

4.7kΩ

NOTE: OP-AMP LEVEL SHIFT CIRCUIT HAS A GAIN OF 0.5 FROM V*.

VIN

TO V+

TO GND PIN

2.5kΩ

7.5kΩ

10kΩ

SEE

NOTE

VIN

4.7µF

ANY DC

Figure 16. Power Supply and Input Connections for Single Supply Operation

MAX260/MAX261/MAX262

Microprocessor Programmable

Universal Active Filters

22 ______________________________________________________________________________________

errors are predictable, the graphs can be used to cor-

rect the selected f0and Q so that the actual realized

parameters are on target. These predicted errors are

not unique to MAX260 series devices and, in fact,

occur with all types of sampled filters. Consequently,

these corrections can be applied to other switched

capacitor filters. In the majority of cases, the errors are

not significant, i.e., less than 1%, and correction is not

needed. However, the MAX262 does employ a lower

range of fCLK/f0ratios than the MAX260 or MAX261 and

is more prone to sampling errors, as the tables show.

Maxim's filter design software applies the previous cor-

rections automatically as a function of desired fCLK/f0,

and Q. Therefore, Figure 20 should not be used when

Maxim's software determines f0and Q. This results in

overcompensation of the sampling errors since the cor-

rection factors are then counted twice.

The data plotted in Figure 20 applies for modes 1 and

3. When using Figure 20 for mode 4, the f0error

obtained from the graph should be multiplied by 1.5

and the Q error should be multiplied by 3.0. In mode 2,

the value of fCLK/f0should be multiplied by √2and the

programmed Q should be divided by √2before using

the graphs.

As with all sampled systems, frequency components of

the input signal above one half the sampling rate are

aliased. In particular, input signal components near the

sampling rate generate difference frequencies that

often fall within the passband of the filter. Such aliased

signals, when they appear at the output, are indistin-

guishable from real input information. For example, the

aliased output signal generated when a 99kHz wave-

form is applied to a filter sampling at 100kHz (fCLK =

200kHz) is 1kHz. This waveform is an attenuated ver-

sion of the output that would result from a true 1kHz

input. Remember that, with the MAX260 series filters,

the nyquist rate (one half the sample rate) is in fact

fCLK/4, because fCLK is internally divided by two.

A simple, passive RC lowpass input filter is usually suf-

ficient to remove input frequencies that can cause

aliasing. In many cases, the input signal itself may be

band limited and require no special anti-alias filtering.

The wideband MAX262 uses lower fCLK/f0ratios than

the MAX260/MAX261 and, for this reason, is more likely

to require input filtering than the MAX260 or MAX281.

Trimming DC Offset

The DC offset voltage at the LP or notch output can be

adjusted with the circuit in Figure 21. This circuit also

uses the input op amp to implement a single-pole anti-

alias filter. Note that the total offset is generally less in

multistage filters than when only one section is used,

MAX261

INABPA

TRACE A

500kHz TTL

TRACE B

A 1V/DIV

B 5mV/DIV

C mV/DIV

1µs/div

TRACE C

C, 1000pF

R, 10kΩ

CLKA

Figure 17. MAX261 Bandpass Output Clock Noise

VIN

CFB

CIN

12pF

~5pF

fCLK

CIN fCLK

RIN =

Figure 18. MAX260 Input Model

VIN

CFB

CA 12pF

0.016pF

~5pF +

fCLK

750 CA fCLK

RIN =

Figure 19. MAX261/MAX262 Input Model

MAX260/MAX261/MAX262

Microprocessor Programmable

Universal Active Filters

______________________________________________________________________________________ 23

since each offset is typical negative and each section

inverts. When the HP or BP outputs are used, the offset

can be removed with capacitor coupling.

Design Examples

Fourth-Order Chebyshev Bandpass Filter

Figure 22 shows both halves of a MAX260 cascaded to

form a fourth-order Chebyshev bandpass filter. The

desired parameters are:

Center frequency (f0) = 1kHz

Pass bandwidth = 200Hz

Stop bandwidth = 600Hz

Max passband ripple = 0.5dB

Min stopband attenuation = 15dB

From the previous parameters, the order (number of

poles) and the f0and Q of each section can be deter-

mined. Such a derivation is beyond the scope of this

data sheet; however, there are a number of sources

that provide design data for this procedure. These

include look-up tables, design texts, and computer pro-

grams. Design software is available from Maxim to pro-

vide comprehensive solutions for most popular filter

configurations. The A and B section parameters for the

above filter are:

f0A = 904Hz f0B = 1106Hz

QA= 7.05 QB= 7.05

To implement this filter, both halves operate in mode 1

and use the same clock. See Tables 2 and 3. The pro-

grammed parameters are:

CLKA= CLKB= 150kHz

fCLK/f0A = 166.50 (Mode 1, N = 42), actual f0A = 902.4Hz

fCLK/f0B = 136.66 (Mode 1, N = 23), actual f0B =

1099.7Hz

QA= QB= 7.11 (Mode 1, N = 119)

Sampling errors are very small at this fCLK/f0ratio, so

the actual realized Q is very close to 7.05 (see Figure

20 or program MPP in the Filter Design Software sec-

tion). Often the realized Q is not exactly the target value

at high Qs because programming resolution lowers as

Q increases. This does not affect most filter designs,

since three-digit Q accuracy is practically never

required, and a Q resolution of 1 is provided up to Qs

of 10. The overall filter gain at f0is 16.4V/V or 24.3dB

(see the Cascading Filters section). If another gain is

required, amplification or attenuation must be added at

the input, output, or between stages.

40 80 10060 120 140 160 180 200

fO ERROR vs. fCLK/fO RATIO (MODE 1, 3)

fCLK/fO RATIO

fO ERROR (%)

Q = 0.512

f0 ERROR IS PLOTTED FOR MODES 1 AND 3

MODE 2: MULTIPLY ICLKIO BY √2 and

DIVIDE Q BY √2 BEFORE USING GRAPH

MODE 4: MUTIPLY fO ERROR BY 1.5

Q = 0.512

-2

-1

-4

-3

-5

-6

-7

40 80 10060 120 140 160 180 200

Q ERROR vs. fCLK/fO RATIO

fCLK/fO RATIO

Q ERROR (%)

Q = 0.5

Q ERROR IS PLOTTED FOR MODES 1 AND 3

MODE 2: MULTIPLY fCLK/fO BY √2 and

DIVIDE Q BY √2 BEFORE USING GRAPH

MODE 4: MUTIPLY Q ERROR BY 1.5

Q = 0.83

Q = 7.11

Q = 3.05

Q = 0.6

Q = 1.21

Figure 20. Sampling Errors in fCLK/f0and Q at Low fCLK/f0and

Q Settings

R2 100kΩ

R3 270kΩ

VIN

+5V

-5V

OFFSET

TRIM

FILTER

INPUT

100kΩ+

R1 100kΩ

NOTE: OP AMP INCLUDED WITH MAX261/MAX262

GAIN = -R1/R2

fLP =1

2πR1C2

Figure 21. Circuit for DC Offset Adjustment

MAX260/MAX261/MAX262

Microprocessor Programmable

Universal Active Filters

24 ______________________________________________________________________________________

In Figure 23, a series of response curves are shown for

the previous configuration using a MAX261 with clock

frequencies ranging from 750kHz to 4MHz (f0from

500Hz to 30kHz). Note that the rightmost curve shows

about 2dB of gain peaking compared to the lower fre-

quency curves, indicating the upper limit of usable filter

accuracy at this Q (see Table 1).

Wide Passband Chebyshev Bandpass

In this example (Figure 24), the desired parameters

are:

Center frequency (f0) = 1kHz

Pass bandwidth = 1kHz

Stop bandwidth = 3kHz

Max passband ripple = 1dB

Min stopband attenuation = 20dB

From the previous parameters, we use either lookup

tables, design texts, or Maxim's filter design programs

to generate the order (number of poles), and the f0and

Q of each second-order section. The A and B parame-

ters are:

f0A = 639Hz f0B = 1564Hz

QA= 2.01 QB= 2.01

To implement this filter, section A operates in mode 1

and section B uses mode 2 to provide a wider overall

range of fCLK/f0ratios. This way, one clock frequency

can drive both sections A and B. See Tables 2 and 3.

CLKA= CLKB= 120kHz

fCLK/f0A = 188.49 (Mode 1, N = 56), actual f0A = 636.6Hz

fCLK/f0B = 76.64 (Mode 2, N = 5), actual f0B = 156.5Hz

QA= 2.000 (Mode 1, N = 96), QB= 2.01 (Mode 2, N =

83)

The overall passband gain at f0is 0.64V/V or

-3.9dB.

High-Frequency Chebyshev Bandpass

The same Chebyshev response shape shown in Figure

24 is implemented at higher frequencies with a

MAX262 in Figure 25. The curves show plots for center

frequencies of 15.6kHz, 31.3kHz, and 47kHz. Not only

is this faster than the MAX260 implementation, but

mode 1 can be used in both halves of the MAX262 for

this filter because the range of available fCLK/f0ratios is

wider with the MAX262 than the MAX260.

11 12

23 21

MAX260

VIN

INABPA

CLKA

CLK PROGRAM

CLKB

INBBPB

WR, AX, DX

VOUT

-60

200 2K1K500 20K10K5K

-35

FREQUENCY (Hz)

GAIN (dB)

PHASE (DEGREES)

-10

-180

180

-90

GAIN

PHASE

Figure 22. Fourth-Order Chebyshev Bandpass Filter

CLKA,B MODE fOA fOB QAQB

150kHz 1 N = 42 N = 23 N = 119 N = 119

-30

1K 10K5K2K 100K50K20K

-15

FREQUENCY (Hz)

GAIN (dB)

Figure 23. MAX261 Fourth-Order Chebyshev Bandpass Using

Coefficients of Figure 22

MAX260/MAX261/MAX262

Microprocessor Programmable

Universal Active Filters

______________________________________________________________________________________ 25

Fourth-Order Butterworth Lowpass

Figure 26 shows a fourth-order Butterworth lowpass

with a cutoff frequency of 3kHz. Sections A and B of a

MAX260 are cascaded. The f0and Q parameters for

each section are:

f0A = 3kHz f0B = 3kHz

QA= 1.307 QB= 0.541

Mode 1 and a 400kHz clock are used. Because of low

Q values, the sampling errors of Figure 20 begin to look

significant in this case. From the graphs, using fCLK/f0

ratio near 133, f0A is about 4% high, f0B is 1.5% high,

QAis -1.2% low, and QBis -0.5% low. If these errors

are not a problem, the corrections can be ignored.

They are included here for best possible accuracy:

CLKA= CLKB= 400kHz

fCLK/f0A = 135.08 (N = 22), f0B = 2961Hz

(-1.3% correction)

fCLK/f0B = 139.80 (N = 25), f0A = 2861Hz

(-4.6% correction)

QA= 1.306 (N = 79, Q resolution prevents +0.5%

correction)

QB= 0.547 (N = 11 +1.1% correction)

Measured wideband noise for this filter is 123µV RMS.

If mode 2 were used, the noise would be 87µV RMS.

For lower noise with either mode, the first section

should have the highest Q (section A in this example).

11 12

23 21

MAX260

VIN

INABPA

CLKA

CLK PROGRAM

CLKB

INBBPB

WR, AX, DX

VOUT

-70

100 1K500200 10K5K2K

-50

FREQUENCY (Hz)

GAIN (dB)

-30

-10

-180

180

PHASE (DEGREES)

-90

GAIN

PHASE

Figure 24. Wide Passband Chebyshev Bandpass Filter

CLKA,B MODEAMODEBfOA fOB QAQB

120kHz 1 2 N = 56 N = 5 N = 96 N = 83

11 12

23 21

MAX262

VIN

INABPA

CLKA

CLK PROGRAM

CLKB

INBBPB

WR, AX, DX

VOUT

-50

1K 10K5K2K 100K50K20K

-40

-30

FREQUENCY (Hz)

GAIN (dB)

-20

-10

fO = 15.6kHz

fCLK = 1MHz

fO = 31.3kHz

fCLK = 2MHz

fO = 47kHz

fCLK = 3MHz

Figure 25. High-Frequency Chebyshev Bandpass Filter

CLKA,B MODE fOA fOB QA QB

1 to 3MHz 1 N = 38 N = 0 N = 96 N = 96

MAX260/MAX261/MAX262

Microprocessor Programmable

Universal Active Filters

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are

implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

26 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600

Ordering Information (continued)

PART TEMP RANGE PACKAGE A C C U R A C Y

MAX261ACNG 0°C to +70°C Plastic DIP 1%

MAX261BCNG 0°C to +70°C Plastic DIP 2%

MAX261AENG -40°C to +85°C Plastic DIP 1%

MAX261BENG -40°C to +85°C Plastic DIP 2%

MAX261ACWG 0°C to +70°C Wide SO 1%

MAX261BCWG 0°C to +70°C Wide SO 2%

MAX261AMRG -55°C to +125°C CERDIP 1%

MAX261BMRG -55°C to +125°C CERDIP 2%

MAX262ACNG 0°C to +70°C Plastic DIP 1%

MAX262BCNG 0°C to +70°C Plastic DIP 2%

MAX262AENG -40°C to +85°C Plastic DIP 1%

MAX2G2BENG -40°C to +85°C Plastic DIP 2%

MAX262ACWG 0°C to +70°C Wide SO 1%

MAX262BCWG 0°C to +70°C Wide SO 2%

MAX262AMRG -55°C to +125°C CERDIP 1%

MAX262BMRG -55°C to +125°C CERDIP 2%

*All devices—24-pin packages 0.3in-wide packages

V+

0.199in

(5.055mm)

CLKACLKB

CLK OUT

N.C.(OP IN)

V-

A0 WR

HPB(N.C.)

N.C.(HPA)

HPA(OP OUT)

N.C.(HPB)

BPALPAINBLPBBPB

0.128in

3.251mm

INA

OSC OUT

GND

NOTE: LABELS IN PARENTHESES ( ) ARE FOR MAX261/MAX262 ONLY

Chip Topography