General Description
The MAX2745 complete single-chip global positioning
system (GPS) RF front-end downconverter utilizes many
innovative and leading-edge RF CMOS design tech-
niques. This high-performance, state-of-the-art device
consumes extremely low power and eliminates the
need for costly SAW and bulky discrete IF filters. The
MAX2745 incorporates a fully integrated low-noise
amplifier (LNA) and mixer, IF section, digital sampler,
and local oscillator synthesizer. The MAX2745 also pro-
vides a voltage supply for an external LNA. In addition,
the MAX2745 features a voltage booster, which can
extend the power-supply voltage to as low as 1.6V.
The MAX2745 supports both 3rd overtone crystal
designs in 32MHz and fundamental frequency crystal
designs in 16MHz, as well as a TCXO implementation.
In addition, the MAX2745 incorporates an on-chip tem-
perature sensor and crystal oscillator with trimmed
capacitors, resulting in a very accurate frequency and
additional system cost savings.
The MAX2745 is available in a space-saving 48-pin
TQFP package and is specified for the extended (-40°C
to +85°C) temperature range. The power consumption
of this device is as low as 41mW at 2.4V.
Applications
In-Vehicle Navigation Systems (IVNSs)
Location-Based Services (PDAs and
Accessories)
Telematics (Vehicle/Asset Tracking and
Inventory Management)
Recreational Handheld/Walkie Talkies
Geographical Information Systems (GISs)
Emergency Roadside Assistance
Emergency Response Systems
Digital Cameras/Camcorders
Consumer Electronics
Features
♦Complete Single-Chip GPS Radio for 16.368MHz
and 32.736MHz Floorplans
♦Single-Ended or Differential Outputs at 4.092MHz
♦Low 3.5dB Typical Noise Figure
♦No External IF SAW or Discrete Filters Required
♦On-Chip Temperature Sensor
♦2.4V to 3.6V Operational Supply Voltage Range
♦Power Consumption as Low as 41mW at 2.4V
♦Wide -40°C to +85°C Operational Temperature
Range
MAX2745
Single-Chip Global Positioning System
Receiver Front-End
________________________________________________________________ Maxim Integrated Products 1
Ordering Information
19-3425; Rev 0; 10/04
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.
EVALUATION KIT
AVAILABLE
PART TEMP RANGE PIN-PACKAGE
MAX2745ECM -40°C to +85°C 48 TQFP-EP*
*EP = Exposed paddle.
Block Diagram/
Pin Configuration
VCXO
BIAS
LNA/MIXER
PFD
DIVIDER
CHG
PUMP
VCO
TEMPERATURE
SENSOR
VSPORT
BANDPASS FILTER
FILTER AUTOMATIC TUNING
AGC QUANTIZER
VOLTAGE
BOOSTER
48
XTALIN
11
VDD
12
AGC_FIL 25 VDD
10
IEXT_LNA
7
RFIN
9
VDD
47
XTALOUT
2
CBIAS
4
30 GND
27 VDD
20
CKOUT
19
VDD_VB
1
RBIAS
3
VDD
VDD
5
GND
13
VDD
14
GND
15
XTAL_SSEL
16
XTAL_CSEL
17
BST_CTRL
18
TEST_EN
21
DOUT
23
VB_CS-
24
VOUT
22
VB_CS+
28 VOUT-
29 VOUT+
31 SCLK
32 VDD
33 COE
34 CFS
35 ODS
36 BPF_CTRL
37
SDATA
38
VTO
39
VDD
40
VTUNE
41
GND
42
CP_OUT
43
VDD
44
GND
46
VDD
6
GND
8
GND
GND
26
45
SHDN
MAX2745
Typical Operating Circuit appears at end of data sheet
MAX2745
Single-Chip Global Positioning System
Receiver Front-End
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
DC ELECTRICAL CHARACTERISTICS
(MAX2745 EV kit, VDD = +2.4V to +3.6V, SHDN = GND, TA= -40°C to +85°C. Typical values are at VDD = +3.0V and TA= +25°C,
unless otherwise noted.)
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.
VDD to GND...........................................................-0.3V to +3.7V
Other Pins to GND......................................-0.3V to (VDD + 0.3V)
RF LNA Input Power .......................................................+10dBm
Continuous Power Dissipation (TA= +70°C)
48-Pin TQFP-EP (derate 12.5mW/°C above +70°C) ............1W
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Soldering Temperature (10s) ...........................................+300°C
PARAMETER CONDITIONS
MIN
TYP
MAX
UNITS
Supply Voltage
2.4
3.6 V
VDD = +3.0V, TA = +25°C (Note 1)
20.5
27 mA
Supply Current Shutdown mode 11 µA
Optional External LNA Supply
Current VDD = +3.0V
10
mA
Logic-Input High Voltage
2.0
V
Logic-Input Low Voltage
0.5
V
Logic-Input Bias Current
-10 +10
µA
AC ELECTRICAL CHARACTERISTICS
(MAX2745 EV kit, VDD = +2.4V to +3.6V, SHDN = GND, TA= -40°C to +85°C. Typical values are at VDD = +3.0V and TA= +25°C,
unless otherwise noted.)
PARAMETER CONDITIONS
MIN
TYP
MAX
UNITS
GENERAL PERFORMANCE
Maximum Conversion Gain (Notes 2, 3) 105
120
dB
Input Frequency
1575.42
MHz
Noise Figure Measured at quantizer output 3.5 dB
Return Loss (S11) -14 dB
LNA/Mixer Input IP3
f1 = 5.09MHz and f2 = 7.09MHz above carrier frequency
-25
dBm
Output IF Frequency
4.092
MHz
OUTPUT STAGE
Differential (VOUT+, VOUT-), CL < 20pF 16
Output Rise/Fall Time Single ended (DOUT), CL<20pF 6 ns
Differential
VDD - 0.9
Output-Voltage-Level Low Single ended 0 V
Differential
Output-Voltage-Level High Single ended VDD V
MAX2745
Single-Chip Global Positioning System
Receiver Front-End
_______________________________________________________________________________________ 3
Note 1: At TA= +25°C, min/max limits are guaranteed by production test.
Note 2: At TA= -40°C, min/max limits are guaranteed by design and characterization.
Note 3: At TA= +25°C and +85°C, min/max limits are guaranteed by production test.
AC ELECTRICAL CHARACTERISTICS (continued)
(MAX2745 EV kit, VDD = +2.4V to +3.6V, SHDN = GND, TA= -40°C to +85°C. Typical values are at VDD = +3.0V and TA= +25°C,
unless otherwise noted.)
PARAMETER CONDITIONS
MIN
TYP
MAX
UNITS
SYNTHESIZER
Fundamental frequency crystal
16.368
Crystal Input Frequency 3rd overtone crystal
32.736
MHz
Charge-Pump Current 0.4 mA
fOFFSET = 10kHz offset,
BWLOOP = 70kHz -81
Phase Noise fOFFSET = 1MHz offset,
BWLOOP = 70kHz
-104
dBc/Hz
Maximum PLL Spur BWLOOP = 70kHz -39 dBc
VCO Tuning Frequency Range (Notes 2, 3)
150
210 270
MHz
VCO Tuning Gain (Notes 2, 3)
150
210 310
MHz/V
IF STAGE
IF Stage Gain VGA set at maximum gain 80 dB
Dynamic Range IF Stage Gain 56 dB
Low-frequency corner 3.1
Bandpass Filter 1dB Corner
Frequency High-frequency corner 5.1
MHz
Bandpass Filter 3dB Bandwidth 2.0
MHz
Bandpass Filter 60dB High-Side
Rejection 6.6
MHz
Bandpass Filter 60dB Low-Side
Rejection 1.6
MHz
Image Rejection 17 dB
In-Band Ripple 1dB
AGC Loop Lock Time 1ms
Typical Operating Characteristics
(MAX2745 EV kit, VDD = +3.0V, SHDN = GND, fRF = 1575.42MHz, and TA= +25°C, unless otherwise noted.)
SUPPLY CURRENT vs. TEMPERATURE
MAX2745 toc01
TEMPERATURE (°C)
SUPPLY CURRENT (mA)
6040200-20
14
18
22
26
30
10
-40 80
VCC = 2.4V
VCC = 2.7V
VCC = 3V
LNA/MIXER GAIN vs. TEMPERATURE
MAX2745 toc02
TEMPERATURE (°C)
LNA MIXER GAIN (dB)
6040200-20
10
5
15
20
25
30
35
40
0
-40 80
VCC = 2.4V VCC = 2.7V
VCC = 3V
IF STAGE GAIN vs. TEMPERATURE
MAX2745 toc03
TEMPERATURE (°C)
IF STAGE GAIN (dB)
6040200-20
70
65
75
80
85
90
95
100
60
-40 80
VCC = 2.4V
VCC = 2.7V
VCC = 3V
MAX2745
Single-Chip Global Positioning System
Receiver Front-End
4 _______________________________________________________________________________________
PIN NAME FUNCTION
1 RBIAS External BIAS Resistor. For normal bias, connect a 100kΩ (1%) resistor to ground.
2 CBIAS BIAS Bypass Capacitor. Connect a 0.1µF capacitor to ground.
3, 4, 9, 11, 13,
25, 27, 32, 39,
43, 46
VDD Power-Supply Voltage. Bypass with a 0.1µF capacitor to ground as close to the pins as possible.
5, 6, 8, 14, 26,
30, 41, 44 GND Ground
7 RFIN RF Input Signal. Requires external matching network.
10
IEXT_LNA
External LNA Voltage Supply
12 AGC_FIL AGC External Filter. Requires external RC lowpass filter.
15
XTAL_SSEL
Crystal Swing Select. Drive logic high for full swing. Drive logic low for limited swing.
16
XTAL_CSEL
Crystal Clock Select. Drive logic high for fundamental mode of 16.368MHz. Drive logic low for third
overtone mode of 32.736MHz.
17
BST_CTRL
Active-High Boost Control Input. Drive logic high to activate the voltage booster (crystal oscillator is
biased from BIAS). Drive logic low to deactivate the voltage booster (crystal oscillator is self-biased).
18 TEST_EN Connect to Ground for Normal Operation
19 VDD_VB Power Supply for Voltage Booster. Connect to VDD if voltage booster is not used.
20 CKOUT Full-Swing Clock Output
21 DOUT Single-Ended Full-Swing Digital Output
22 VB_CS+ Positive Voltage Booster External Floating CAP. Connect a 6nF capacitor to GND.
23 VB_CS- Negative Voltage Booster External Floating CAP. Connect a 6nF capacitor to GND.
24 VOUT Voltage Booster Output. Bypass to GND with a 1µF capacitor as close to the pin as possible.
Pin Description
Typical Operating Characteristics (continued)
(MAX2745 EV kit, VDD = +3.0V, SHDN = GND, fRF = 1575.42MHz, and TA= +25°C, unless otherwise noted.)
TOTAL GAIN vs. TEMPERATURE
MAX2745 toc04
TEMPERATURE (°C)
TOTAL GAIN (dB)
6040200-20
102
104
106
108
110
100
-40 80
VCC = 2.4V
VCC = 2.7V
VCC = 3V
0
0.4
0.2
0.8
0.6
1.4
1.2
1.0
1.6
-40 0-20 20 40 60 80
TEMPERATURE-SENSOR OUTPUT VOLTAGE
vs. TEMPERATURE
MAX4725 toc05
TEMPERATURE (°C)
TEMPERATURE-SENSOR OUTPUT VOLTAGE, VTO (V)
VDD = 3.6V
VDD = 2.4V
2.0
2.4
2.2
2.8
2.6
3.0
3.2
1.6 1.9 2.01.7 1.8 2.1 2.2 2.3
VOLTAGE-BOOSTER
OUTPUT vs. VDD_VB
MAX2745 toc06
VDD_VB (V)
VOLTAGE-BOOSTER OUTPUT, VOUT (V)
TA = -40°C
BST_CTRL = HIGH
VOUT = VDD
TA = +25°C
TA = +85°C
MAX2745
Single-Chip Global Positioning System
Receiver Front-End
_______________________________________________________________________________________ 5
PIN NAME FUNCTION
28 VOUT- Quantizer Analog Negative Limited-Swing Output
29 VOUT+ Quantizer Analog Positive Limited-Swing Output
31 SCLK Serial Port Clock Input (Bidirectional PAD)
33 COE Clock Output Enable. Drive logic high to enable the clock output. Drive logic low to disable the clock
output.
34 CFS Clock Frequency Select. Drive logic high to select 16MHz. Drive logic low to select 32MHz.
35 ODS Output Data Select. Drive logic high to select full-swing output. Drive logic low to select limited-
swing output.
36
BPF_CTRL
Bandpass Filter (BPF) Control. Drive logic high to activate the tuning block control BPF. Drive logic
low to let BPF be controlled by fuses.
37 SDATA Serial Port Data (Bidirectional PAD)
38
TEMPOUT
Temperature Sense DC Voltage Output
40 VTUNE VCO Tuning Input
42 CP_OUT PLL Charge-Pump Output. Analog high-impedance output. Current source. Connect directly to the
PLL loop filter input.
45 SHDN Active-High Shutdown Input. Drive logic low to disable all device functions. Drive logic high for
normal operation.
47
XTALOUT
Crystal Output. Connect directly to the external crystal.
48 XTALIN Crystal Input. Connect directly to the external crystal or TCXO.
Pin Description (continued)
Functional Diagram
IMAGE
REJECTION
BPF
VGA
AGC
TEMP
SENSOR
DIGITAL
CONTROL
VOLTAGE
BOOSTER
POWER
SWITCH
BPF
1.57542GHz
SHUTDOWN
VDD1V6
VSPORT TEMP
SENSOR DC
OUTPUT
PLL LOOP
FILTER
/96
/48 PFD
LNA
CP MUX
CLOCK
FREQ
CONTROL
CLOCK
OUTPUT
CONTROL
CLOCK OUTPUT:
16.368MHz
32.768MHz
16.368MHz
32.768MHz
QUANTIZER
4.092MHz IF OUTPUT:
FULL SWING
DIFFERENTIAL
LIMITED SWING
OUTPUT
CONTROL
MAX2745
MAX2745
Single-Chip Global Positioning System
Receiver Front-End
6 _______________________________________________________________________________________
Detailed Description
The MAX2745 complete single-chip GPS front-end
downconverter utilizes many innovative and leading-
edge RF CMOS design techniques. This high-perfor-
mance, state-of-the-art device consumes extremely low
power and eliminates the need for costly SAW and
bulky discrete IF filters. The MAX2745 incorporates a
fully integrated LNA/mixer, IF section, digital sampler,
and local oscillator synthesizer. The MAX2745 also pro-
vides voltage supply for an external LNA. In addition,
the MAX2745 features a voltage booster that can
extend the power-supply voltage to as low as 1.6V.
The MAX2745 supports both 3rd overtone crystal
designs in 32MHz and fundamental frequency crystal
design in 16MHz, as well as a TCXO implementation. In
addition, the MAX2745 incorporates an on-chip tempera-
ture sensor and crystal oscillator with trimmed capaci-
tors, resulting in a very accurate frequency and
additional system cost savings.
The MAX2745 also incorporates a 2MHz bandwidth
bandpass filter to reduce off-band noise. The band-
width and the center frequency of the bandpass filter
are guaranteed by an advanced tuning scheme.
The MAX2745 is offered in a space-saving 48-pin TQFP
package. The operational temperature range is speci-
fied from -40°C to +85°C. The power consumption of
this device is as low as 41mW at 2.4V.
LNA/Mixer
The RF input signal from the GPS antenna is fed
through an LNA with a gain of 20dB. The amplified sig-
nal is then fed to a mixer that downconverts the signal
(1575.42MHz) to a quadrature differential IF of
4.092MHz.
IF Stage
The quadrature IF signals pass through the IF filter,
which rejects the out-of-band spurs by more than 60dB
and the image noise by 17dB (typ). After the image
reject filter, the signal is converted from quadrature to
differential. The filtered IF signal is then amplified by
the AGC block, which sets the VGA output signal level
to a predetermined value through the application using
56dB of dynamic range.
IF Output Selection
The sampled outputs of the GPS signal are available in
a single-ended or limited-differential format. The ODS
pin controls the output format.
Synthesizer
An on-chip VCO provides quadrature differential LO
signals to the downconverting mixer. An on-chip crystal
oscillator driver generates the reference frequency. The
integrated synthesizer includes the VCO, crystal oscil-
lator driver, main frequency divider, phase-frequency
detector, and charge pump. It uses an off-chip PLL
loop filter and crystal. If a TCXO is used, connect the
output of the TCXO to XTALIN.
The main division ratio for the synthesizer is 96 or 48.
With this division ratio, a low-side injection LO can be
used with a 16.368MHz or 32.736MHz crystal. Note that
if a 3rd overtone crystal is used for the 32.736MHz, an
off-chip notch filter to reject the fundamental frequency
is required. The notch filter can be built with one induc-
tor and one capacitor.
Control Block
This block is used mainly for testing purposes and to
set the internal trimmed capacitor. This block is pro-
grammed through the VSport.
VSport Serial Data Interface
The serial interface within the MAX2745 is used by the
baseband to communicate control signals and is also
used for internal testing of the device. (This serial port
is described in a separate document, which is available
upon request.)
Trimmed VCXO Frequency
An on-chip, trimmed capacitor with a temperature coeffi-
cient of better than 30ppm/°C is used to compensate for
the component variation of the reference frequency
associated circuitry. The value of the capacitor is pro-
grammed in 512 binary steps and ranges from a mini-
mum of 80fF to a maximum of 40pF, ±20%. Pro-
gramming is accomplished with the VSport serial inter-
face. The no load capacitance on the crystal out follows
the equation:
C(no load) = ([Register Value] x 40/512) pF
Upon power-up, the capacitor value is set to the mini-
mum value. This enables the MAX2745 to work with an
off-chip, trimmed capacitor. If the baseband has the
capability of programming the radio, the off-chip,
trimmed capacitor can be omitted by setting the inter-
nal trimmed capacitor through the VSPORT.
MAX2745
Single-Chip Global Positioning System
Receiver Front-End
_______________________________________________________________________________________ 7
Temperature Sensor
The MAX2745 features an on-chip temperature sensor to
facilitate system temperature compensations in conjunc-
tion with the trimmed capacitor. This circuit generates an
output voltage at TEMPOUT, which is used to approxi-
mate the temperature by the following equation:
T = TO+ (VOUT - VOUT,TO)/SG
where SG is the sensor gain, TOis factory-trimmed tem-
perature, which can be any value (normally +27°C), and
VOUT is the temperature output voltage at TO. The coeffi-
cient SG in the above equation is targeted to be between
6mV/°C and 8mV/°C, depending on the temperature.
Voltage Booster
The MAX2745 integrates an internal voltage booster to
allow proper operation with supply voltages as low as
1.6V. The circuit includes two 6nF floating external
capacitors connected to VB_CS±(pins 22 and 23) and
a 1µF capacitance to VOUT (boosted voltage output,
pin 24). To reduce the output voltage ripple, use an
external LC lowpass filter, which can be built with two
inductors and one capacitor.
Applications Information
Operation with Voltage Booster
Under normal operating conditions, the recommended
power-supply voltage ranges from 2.4V to 3.6V. But
with the integrated voltage booster on-chip, the
MAX2745 can be powered from power-supply voltages
as low as 1.6V, and only requires a minimal number of
external components. This is not the most efficient
operating mode, since the power efficiency will be low-
ered to less than 50%.
As described in the Detailed Description section, to use
the voltage booster, connect 6nF floating capacitors to
VB_CS±, pins 22 and 23, and 1µF bypass capacitor to
VOUT, pin 24. Connect VOUT (pin 24) to all the power-
supply (VDD) pins and pull BST_CTRL, pin 17, high to
activate the booster. Then the MAX2745 can be pow-
ered from supply voltages ranging from 1.6V to 2.3V at
VDD_VB, pin 19, and the voltage booster output can
source up to 25mA current. It is recommended that the
voltage booster be used as a backup supply. To do
this, additional circuits including a voltage monitor and
a switch are needed. These components are inexpen-
sive and can be found in the Maxim product family.
Layout Issues
A properly designed PC board is an essential part of
any RF/microwave circuit. Use the MAX2745 EV kit as a
guide. Use controlled-impedance lines on all frequency
inputs and outputs. Use low inductance connections to
ground on all ground pins and wherever the compo-
nents are connected to ground. Place decoupling
capacitors close to all VCC connections. For proper
operation, connect the metal exposed paddle at the
back of the IC to the PC board ground plane with multi-
ple vias.
Chip Information
TRANSISTOR COUNT: 9205
PROCESS: CMOS
MAX2745
Single-Chip Global Positioning System
Receiver Front-End
8 _______________________________________________________________________________________
Typical Application Circuit
VCXO
BIAS
LNA/MIXER
PFD
DIVIDER
CHG
PUMP
VCO
TEMPERATURE
SENSOR
VSPORT
BANDPASS FILTER
FILTER AUTOMATIC TUNING
AGC QUANTIZER
VOLTAGE
BOOSTER
1
2
3
4
5
6
7
8
9
10
11
12
36
35
34
33
32
31
30
29
28
27
25
13 14 15 16 17 18 19 20 21 22 23 24
48 47 46 45 44 43 42 41 40 39 38 37
XTALIN
VDD
AGC_FIL VDD
IEXT_LNA
RFIN
fIN
VDD
XTALOUT
CBIAS
VDD
GND
VDD
CKOUT
VDD_VB
RBIAS
VDD
GND
VDD
GND
XTAL_SSEL
XTAL_CSEL
BST_CTRL
TEST_EN
DOUT
VB_CS-
V
OUT
VB_CS+
GND
VOUT-
VOUT+
SCLK
VDD
COE
CFS
ODS
BPF_CTRL
SDATA
TEMPOUT
V
DD
VTUNE
GND
CP_OUT
V
DD
GND
V
DD
GND
GND
1575.42MHz
26
SHDN
MAX2745
TCXO
OPTIONAL XTAL INPUT
PIN 47
PIN 48
MAX2745
SSingle-Chip Global Positioning System
Receiver Front-End
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 _____________________ 9
© 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
48L,TQFP.EPS
F
1
2
21-0065
PACKAGE OUTLINE,
32/48L TQFP, 7x7x1.0mm EP OPTION
F
2
2
21-0065
PACKAGE OUTLINE,
32/48L TQFP, 7x7x1.0mm EP OPTION