AMI IZ STANDARD PRODUCTS $2559E/F February 1993 Features Wide Operating Supply Voltage Range: 2.5 to 10 Volts Low Power CMOS Circuitry Allows Device Power to be Derived Directly from the Telephone Lines or from Small Batteries, e.g., 9V Uses TV Crystal Standard (3.58MHz) to Derive all Frequencies thus Providing Very High Accuracy and Stability Mute Drivers On-Chip Interfaces Directly to a Standard Telephone Push- Button or Calculator Type X-Y Keyboard The Total Harmonic Distortion is Below Industry Specification DTMF Tone Generator Oscillator Resistor On Chip * On-Chip Generation of a Reference Voltage to Assure Amplitude Stability of the Dual Tones Over the Operating Voltage and Temperature Range * Single Tone as Well as Dual Tone Capability Two Options Available: E: Mode Select F:Chip Disable The S2559 DTMF Generator is specifically designed to implement.a dual tone telephone dialing system. The device can interface directly to a standard pushbutton Block Diagram Pin Configuration *oo Vop 01 xTAL =f >| ] | 2 | XMIT 5 OSCILLATOR +2 TRANSMIT MUTE 2] asamuz { a | f > ha] mute TFT INH 4 FO Vo (] 1 16 [7] TONE OUT | | at [rape] LI | | xmiT (] 2 15 |] MOSL/cD nz [1a}+>] now KevaoaRo aenwioen | 8h 8 STAGE or | 3 14 [7] Ry n3 [12> toGic ew SROUF COUNTER NETWORK eC] 4 13k, na [ir] I fen | $2559 | lt ee 12 [7 Rs | comwost [15] occ, +H & ADDER Vss [] 6 11 J Ra ry a ose; (} 7 10 [7] MUTE t1 Ek cK EN | y, Osc, Cl 8 9 [_] C a2 oo 0 4 c2[abery conunn PROS AMABLE Tet, | 8 STAGE nesisran | | c3 [5 }e>{xevgoanp Locic oan taro eB T | counter werwonk [7 a 2] . | | [16] TONE OUT Lo Z Veg [5]$2599E/F AMI iZ STANDARD PRODUCTS DIMF Tone Generator General Description (Continued) telephone keyboard or calculator type X-Y keyboard and operates directly from the telephone lines. All necessary dual-tone frequencies are derived from the widely used TV crystal standard providing very high ac- curacy and stability. The required sinudsoidal wave- form for the individual tones is digitally synthesized on the chip. The waveform so generated has very low total harmonic distortion. A voltage reference is generated on the chip which is stable over the operating voltage Absolute Maximum Ratings February 1993 and temperature range and regulates the signal levels of the dual tones to meet the recommended telephone industry specifications. These features permit the $2559 to be incorporated with a slight modification of the standard 500 type telephone basic circuitry to form a pushbutton dual-tone telephone. Other applications of the device include radio and mobile telephones, remote control, Point-of-Sale, and Credit Card Verifica- tion Terminals and process control. DC Supply Voltage (Vpp-Vss) bce eee eee ete e eee Ln beeen e ett teen ener ees + 10.5V Operating Temperature ........................0.0. Com-0C to + 70C, Ind-45C to + 85C, Mil--55 to + 125C Storage Temperature .............0... 0... cere eee eee Power Dissipation at 25C ...........0..0...0. 0.00222. Ta) . | Ltn nee eee terete renee ees 30C to + 125C $2559E/F Electrical Characteristics: Symbol Parameter/Conditions oe a Min. Typ. Max. Units Supply Voltage Tone Out Mode (Valid Key Depressed) 25 10.0 V Voo NonTone Out Mode (No Key Depressed) 16 10.0 V Supply Current Standby ( No Key Selected, Tone, XMIT 3.0 0.3 30 pA loo and MUTE Outputs Unioaded) 100 10 400 yA Operating ( One Key Selected, Tone, XMIT 3.0 1.0 2.0 mA and MUTE Outputs Unioaded) 10.0 8 16.0 mA ToneOutput Com 335 Com 565 Single Tone Row Tone, RL = 390Q 35 Ind 255 465 Ind 660 mVims SO56QE/F Mil 235 Mil 700 Com 380 Mode Output 5.0 Ind 300 540 710 mVrms Mil 250 Com 380 Vor Voltage Row Tone, RL = 2400 10.0 tnd 300 550 735 mVrms Mil 250 dBcr Ratio of Column to Row Tone (Dual Tone Mode) 2559E/F 3.5-10.0 10 2.0 3.0 dB %DIS Distortion * 2559E/F 3.5-10.0 7 %IZ STANDARD PRODUCTS | S2559E/F February 1993 DTMF Tone Generator $2559E/F Electrical Characteristics: (continued) Symbol Parameter/Conditions (on-tss) Min. Typ. Max. Units XMIT, MUTE Outputs V, XMIT, Output Voltage, High (lo = 15mA) 3.0 1.5 1.8 OH (No Key Depressed){Pin 2} (lo4 = 50mA) 10.0 8.5 8.8 lor XMIT, Output Source Leakage Current, Vop =0V 10.0 100 pA V MUTE (Pin 10) Output Voltage, Low, 2.75 0 0.5 OL (No Key Depressed), No Load 10.0 0 0.5 V MUTE, Output Voltage, High, 2.75 2.5 2.75 oH (One Key Depressed) No Load 10.0 9.5 10.0 lo MUTE, Output Sink VoL =0.5V 3.0 0.53 1.3 mA Current 10.0 2.0 5.3 mA lon MUTE, Output Source Vou = 2.5V 3.0 0.17 0.41 mA Current Vou =9.5V 10.0 0.57 1.5 mA Distortion is defined as the ratio of the total power of all extraneous frequencies, in the VOICE and above 500Hz, to the total power of the DTMF frequency pair. Table 1. Comparisons of Specified vs Actual Tone Frequencies Generated by $2559 Table 2. XMIT and MUTE Output Functional Relationship OUTPUT FREQUENCY Hz ACTIVE % ERROR OUTPUT DIGIT KEY INPUT SPECIFIED ACTUAL SEE NOTE RELEASED | vepressen | DIGIT KEY | = COMMENT R1 697 699.1 +0.30 R2 770 766.2 ~0.49 XMIT Vop High Can source at least R3 852 847.4 0.54 Impedance 50mA at 10V with R4 941 948.0 +0.74 1.5V max. drop C1 1,209 1,215.9 +0.57 C2 1,336 1,331.7 0.32 C3 1,477 1,417.9 0.35 MUTE Vss Vop Can source or C4 1,633 1,645.0 +0.73 sink current NOTE: % Error does not include oscillator drift.S2559E/F AMI iZ STANDARD PRODUCTS DTMF Tone Generator February 1993 Figure 1. Standard Telephone Push Button Keyboard ? -O--O--O --O-O- 4 eo Ry -O-O--O-- COMMON <O-7 2 : Ron (Contact Resistance) < 1kQ (CONNECT TO Vpp OR LEAVE FLOATING) C3 MECHANICAL LINKAGE O77 Circuit Description The $2559 is designed so that it can be interfaced easi- ly to the dual tone signaling telephone system and that it will more than adequately meet the recommended telephone industry specifications regarding the dual tone signaling scheme. Design Objectives The specifications that are important to the design of the DTMF Generator are summarized below: the dual tone signal consists of linear addition of two voice fre- quency signals. One of the two signals is selected from a group of frequencies called the Low Group and the other is selected from a group of frequencies called the High Group. The low group consists of four frequen- cies 697, 770, 852 and 941 Hz. The high group consists of four frequencies 1209, 1336, 1477 and 1633 Hz. A keyboard arranged in a row, column format (4 rows x 3 or 4 columns) is used for number entry. When a push button corresponding to a digit (0 thru 9) is pushed, one appropriate row (R1 thru R4) and one appropriate col- umn (C1 thru C4) is selected. The active row input selects one of the low group frequencies and the active column input selects one of the high group frequen- cies. In standard dual tone telephone systems, the highest high group frequency of 1633Hz (Col. 4) is not used. The frequency tolerance must be + 1.0%. How- ever, the $2559 provides a better than .75% accuracy. The total harmonic and intermodulation distortion of the dual tone must be less than 10% as seen at the tele- phone terminals. (Ref. 1.) The high group to low group signal amplitude ratio should be 2.0 + 2dB and the absolute amplitude of the low group and high group tones must be within the allowed range. (Ref. 1.) These requirements apply when the telephone is used over a short loop or long loop and over the operating tempera- ture range. The design of the $2559 takes into account these considerations. Oscillator The device contains an oscillator circuit with the necessary parasitic capacitances and feedback resistor on chip so that it is only necessary to connect a standard 3.58MHz TV crystal across the OSC, and OSCo terminals to implement the oscillator function. The oscillator functions whenever a row input is acti- vated. The reference frequency is divided by 2 and then drives two sets of programmable dividers, the high group and the low group.AM I Z STANDARD PRODUCTS $2559E/F February 1993 Keyboard Interface The $2559 employs a calculator type scanning circuitry to determine key closures. When no key is depressed, active pull-down resistors are on on the row inputs and active pull-up resistors are on on the column in- puts. When a key is pushed a high level is seen on one of the row inputs, the oscillator starts and the keyboard scan logic turns on. The active pull-up or pull-down resistors are selectively switched on and off as the keyboard scan logic determines the row and the col- umn inputs that are selected. The advantage of the scanning technique is that a keyboard arrangement of SPST switches are shown in Figure 2 without the need DITMF Tone Generator for a common line, can be used. Conventional tele- phone push button keyboards as shown in Figure 1 or X-Y keyboards with common can also be used. The common line of these keyboards can be left uncon- nected or wired high. Logic Interface The S2559 can also interface with CMOS logic outputs directly. The $2559 requires active High logic levels. Since the active pull-up resistors present in the $2559 are fairly low value (5002 typ), diodes can be used as shown in Figure 3 to eliminate excessive sink current flowing into the logic outputs in their Low state. SPST MATRIX KEYSORTED: Os fs ] Figure 2. SPST Matrix Keyboard Arranged in the 2 of 8 Row, Column Format 1 R1 v R2 R3 R4 C4 (OPTIONAL COLUMN) Tone Generation When a valid key closure is detected, the keyboard logic programs the high and low group dividers with appropriate divider ratios so that the output of these dividers cycle at 16 times the desired high group and low group frequencies. The outputs of the program- mable dividers drive two 8-stage Johnson counters. The symmetry of the clock input to the two divide by 16 Johnson counters allows 32 equal time segments to be generated within each output cycle. The 32 segments are used to digitally synthesize a stair-step waveform to approximate the sinewave function (see Fiqure 3). This is done by connecting a weighted resistor ladder net- work between the outputs of the Johnson counter, Vop and Veer. Vrer Closely tracks Vpp over the operating voltage and temperature range and therefore the peak- to-peak amplitude Vp (Vpp Vref) of the stairstep func- tion is fairly constant. Vper is so chosen that Vp falls within the allowed range of the high group and low group tones.S2599E/F STANDARD PRODUCTS DIMF Tone Generator February 1993 Figure 3. Logic Interface for Keyboard Inputs of the $2559 ? Vop oo D1 > > 14 R, NN > 13], a 2 Ny, 12], i 3 > 11 Ry $2559 > 3 C, pte. Dt hes 9 Cy D8 Vg Vss I G G1 THRU G8 ANY TYPE CMOS GATE D1 THRU D8 DIODES TYPE IN914 2,3,4,5 ! 7,8, 9 10,14 12; 13,14 5 Figure 4. Stairstep Waveform of the Digitally Synthesized Sinewave 16 7 18,1920 21, 22,2324 25 26 27 28 29 30/31, 32 (Yop) 1.05 094 os 07+ > a w 064 3 <x = 05-7 e oS 2 044 0.3 02 014 (Ves) TIME SEGMENTS yAMI IZ STANDARD PRODUCTS $2559E/F February 1993 The individual tones generated by the sinewave synthe- sizer are then linearly added and drive a bipolar NPN transistor connected as emitter follower to allow pro- per impedance transformation, at the same time preser- ving signal level. Dual Tone Mode When one row and one column is selected dual tone output consisting of an appropriate low group and high group tone is generated. If two digit keys, that are not either in the same row or in the same column, are de- pressed, the dual tone mode is disabled and no output is provided. Single Tone Mode Single tones either in the low group or the high group can be generated as follows. A low group tone can be generated by activating the appropriate row input or by depressing two digit keys in the appropriate row. A high group tone can be generated by depressing two digit keys in the appropriate column, i.e., selecting the appropriate column input and two row inputs in that column. Mode Select The S2559E has a Mode Select (MDSL) input (Pin 15). When MDSL is left floating (unconnected) or connected to Vpp, both the dual tone and single tone modes are available. If MDSL is connected to Vsg, the single tone mode is disabled and no output tone is produced if an attempt for single tone is made. The S2559F does not have the Mode Select option. Chip Disable The S2559F has a Chip Disable input at Pin 15 instead of the Mode Select input. The chip disable for the S2559F is active high. When the chip disable is ac- tive, the tone output goes to Vsg, the row, column in- puts go into a high impedance state, the oscillator is in- hibited and the MUTE and XMIT outputs go into active Quartz Crystal Specification (25 C + 2C) Operating Temperature Range: 0C to + 70C Frequency ...........0....0 0.000... 3.579545MHz Frequency Calibration Tolerance..................., 024% Load Capacitance... eee, 18pF Effective Series Resistance.................,. 180 Ohms, max. Drive Level-Correlation/Operating..........00......... 2mw Shunt Capacitance.......0.......0.000.....00., 7pF, max. Oscillation Mode.................0.....000., Fundamental DTMF Tone Generator states. The effect is the device essentially disconnects from the keyboard. This allows one keyboard to be shared among several devices. The CD pin has an internal pull-down. MUTE, XMIT Outputs The S2559E, F have a CMOS buffer for the MUTE output and a bipolar NPN transistor for the XMIT output. With no keys depressed, the MUTE output is low and the XMIT output is in the active state so that substantial current can be sourced to a load. When a key is depressed, the MUTE output goes high, while the XMIT Output goes into a high impedance state. When Chip Disable is high the MUTE output is forced low and the XMIT output is in active state regardless of the state of the keyboard inputs. Amplitude/Distortion Measurements Amplitude and distortion are two important parameters in all applications of the Digital Tone Generator. Ampli- tude depends upon the operating supply voltage as well as the load resistance connected on the Tone Out- put pin. The on-chip reference circuit is fully operation- al when the supply voltage equals or exceeds 5 volts and as a consequence the tone amplitude is regulated in the supply voltage range above 5 volts. The load resistor value also controls the amplitude. If R; is low the reflected impedance into the base of the output transistor is low and the tone output amplitude is lower. For R, greater than 5kQ the reflected impedance is suf- ficiently large and highest amplitude is produced. Indi- vidual tone amplitudes can be measured by applying the dual tone signal to a wave analyzer (H-P type 3581A) and amplitudes at the selected frequencies can be noted. This measurement also permits verification of the preemphasis between the individual frequency tones. Distortion is defined as the ratio of the total power of all extraneous frequencies in the voiceband above 500Hz accompanying the signal to the power of the fre- quency pair. This ratio must be less than 10% or when expressed in dB must be lower than 20dB. (Ref. 1.) Voiceband is conventionally the frequency band of 300Hz to 3400Hz. Mathematically distortion can be expressed as: Vi (Wy)2 + (Wa)? +. . + (Vy)2 Dist. = (Vi)? + (Vy)2 where (V1). . (Vy) are extraneous frequency (i.e., inter- modulation and harmonic) components in the 500Hz to$2559E/F AMI IZ STANDARD PRODUCTS DIMF Tone Generator 3400Hz band and V,_ and V,, are the individual frequency components of the DTMF signal. The expression can be expressed in dB as: V (Wy)2 + (V2)2 +. . (Vy)2 Ve (Vi)? + (Vu)? = 10 log[ (Vj)2 + ..(Vy)2] log] (VL)2 + (VL)2 + (Vu)2]}---(1) An accurate way of measuring distortion is to plot a spectrum of the signal by using a spectrum analyzer (H-P type 3580A) and an X-Y plotter (H-P type 7046A). In- dividual extraneous and signal frequency components are then noted and distortion is calculated by using the expression (1) above. Figure 6 shows a spectrum plot of a typical signal obtained from a S2559 device operating from a fixed supply of 4Vdc and R, = 10k in the test circuit of Figure 5. Mathematical analysis of the spec- DISTyp = 20 log February 1993 trum shows distortion to be 30dB (3.2%). For quick estimate of distortion, a rule of thumb as outlined below can be used. As a first approximation distortion in dB equals the dif- ference between the amplitude (dB) of the extraneous component that has the highest amplitude and the amplitude (dB) of the low frequency signal. This rule of thumb would give an estimate of 28dB as distortion for the spectrum plot of Figure 6 which is close to the computed result of 30dB. In a telephone application amplitude and distortion are affected by several factors that are interdependent. Ref. 1: Bell System Communications Technical Refer- ence, PUB 47001, Electrical Characteristics of Bell System Network Facilities at the Interface with Voice- band Ancillary and Data Equipment, August 1976. SIG Figure 5. Test Circuit for Distortion Measurement Vy TONE | 16 po OUT 2 MOSL | 15 + y XMIT to + D as Ct Ri 4 LOW IMPED. Vv oe M $2559 POWER 4 3 SUPPLY Sj 02 Ry - ; 3 63 R3 H2 6 Vss Ra a u Osc; mute 3.579545MHz CRYSTAL 8 osc, ty EE SPECTRUM XY ANALYZER PLOTTER HP HP TYPE TYPE 3580A 7046A Xour Xin 3 Ry = 10k P Your Yin GNDMAMI S2559E/F STANDARD PRODUCTS February 1993 DIMF Tone Generator Figure 6. A Typical Spectrum Plot 1 ________-_ volcepanp ________________.__J Va (-1.5) J) Ve (4.5) 5k 7 -10 E 1 Y DEVICE = $2559D ask YY TEMP = ROOM 1 VY (Vp ~ Vss) = 4V DC FIXED 7 Ri = 10k 20 TEST CKT = FIGURES Y -25 E 2 Y 1 -30 /) V2 (-32) 3 35 4 V5 (-36) So / E 1 z 40 E Z / Y V3 (-44) 45 1 Vi (-48) Va (-47) Ve (an y 50 F J iY 55 J) 4 -60 1 y -65 L J N | t ! ! t | i 0 05 1.0 15 2.0 25 3.0 35 40 45 5.0 FREQUENCY (KHz) >