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19-1670; Rev 0; 4/00
Integrated GPS Receiver and Synthesizer
General Description
The MAX2740 is a complete global positioning system (GPS) receiver from antenna output to digitizer input. The signal path includes the LNA, two downconverters, and variable-gain and fixed-gain amplifiers. By utilizing a double-conversion superheterodyne architecture with external surface acoustic wave (SAW) filters, high levels of image rejection and blocking immunity are possible. Receiver linearity has been maximized to improve operation in hostile RFI environments found in cellular base stations. The MAX2740 also includes a high-performance voltage-controlled oscillator (VCO) with low phase noise for subcentimeter carrier phase applications, and a fixed-frequency synthesizer for generation of all required on-chip local oscillators. The unique frequency plan captured in the MAX2740 is suitable for joint GPS/GLONASS receivers with minimal external components. This allows the MAX2740 to provide a cost-effective and high-performance solution for navigation and timing products that need maximum satellite availability. The MAX2740 is compatible with a high-performance DSP engine capable of very fast time to first fix and excellent multipath rejection.
Features
o High Selectivity for Hostile Base Station Environments o Complete Antenna-to-Baseband Receiver Solution o >100dB Total Receiver Gain Including All Filter Losses o >50dB Automatic Gain Control (AGC) Range o Fully Balanced Topology for Minimum Spurious Responses o Low Phase Noise VCO for Carrier Phase Applications o Compatible with High-Performance Companion DSP
MAX2740
Ordering Information
PART MAX2740ECM *Exposed paddle TEMP. RANGE -40C to +85C PIN-PACKAGE 48 TQFP-EP*
________________________Applications
Base Station Timing E911 Location Assistance GPS Automotive and Consumer Receivers Wireless Local-Loop Timing Joint GPS/GLONASS Receivers High-Precision Timing for SDH Networks High-Positional-Accuracy Surveying Equipment
GND GND LNA_IN GND GND GND RFMIX_INGC VCC_ANA GND GND VCC_VCO
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Pin Configuration/ Functional Diagram
LNA_OUT GND RFMIX_IN+ VCC_RFMIX RFMIX_OUT+ RFMIX_OUTGND GND VCC_IFMIX IFMIX_IN+ IFMIX_INGND
48 47 46 45 44 43 42 41 40 39 38 37
36 35 34 33 32 31 30 29 28 27 26 25 17 18 19 20 21 22 23 24
MAX2740
/2 /8 /6 /6 PFD
IFMIX_OUT+ IFMIX_OUTVGA_IN+ VGA_INGND VGA_OUT+ VGA_OUTGND FGA_IN+ FGA_INGND FGA_OUT+
48 TQFP ACTUAL SIZE 9mm x 9mm
________________________________________________________________ Maxim Integrated Products
TANK GND GND VCC_DIG DOWN UP GLS_OUT REF_IN GND GND GND FGA_OUT-
TQFP-EP
1
For free samples and the latest literature, visit www.maxim-ic.com or phone 1-800-998-8800. For small orders, phone 1-800-835-8769.
Integrated GPS Receiver and Synthesizer MAX2740
ABSOLUTE MAXIMUM RATINGS
VCC Pins to GND ...................................................-0.3V to +4.3V RF LNA Input Power .......................................................+10dBm LO Input Power...............................................................+10dBm GC Input Voltage ..........................................-0.3 to (VCC + 0.3V) Continuous Power Dissipation (TA = +85C) 48-Pin TQFP-EP Package ...........................................800mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +160C Lead Temperature (soldering, 10s) .................................+300C
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.
DC ELECTRICAL CHARACTERISTICS
(VCC = +2.7V to +3.3V, TA = -40C to +85C. Typical values are at VCC = +3.0, TA = +25C.)
PARAMETER Total Supply Current AGC Voltage Range AGC Current -50 CONDITIONS MIN TYP 55.1 0.5 to 2.5 +25 MAX 84.3 UNITS mA V A
AC ELECTRICAL CHARACTERISTICS
(MAX2740 EV kit, VCC = +3.0V, 50 system impedance, FRF = 1575.42MHz, FIF1 = 135.42MHz, FIF2 = 15.42MHz, FREF = 20MHz at 600mVpp, TA = +25C, unless otherwise noted.)
PARAMETER LNA LNA Gain LNA Gain Variation Over Temperature LNA Input Third-Order Intercept Point LNA Noise Figure RF MIXER (Zl = 100 differential) RF Mixer Conversion Gain RF Mixer Input IP3 RF Mixer Noise Figure (SSB) IF MIXER (Zs = 100 differential, Zl = 4k differential) IF Mixer Conversion Gain VARIABLE-GAIN AMPLIFIER (VGA) (Zl = 4k differential) VGA Voltage Gain at Maximum Gain Setting VGA Voltage Gain at Minimum Gain Setting FIXED GAIN AMPLIFIER (FGA) FGA Voltage Gain FGA 1dB Compression (Output) GC = 2.5V GC = 0.5V 15.1 -54.7 dB dB 36.3 dB (Note 3) 22.6 -22.4 11.0 dB dBm dB (Note 1) Relative to ambient (Note 1) (Note 2) 13.1 -1.3 16.0 0.5 -9.4 2.6 17.2 +1.0 dB dB dBm dB CONDITIONS MIN TYP MAX UNITS
Zl = 4k differential
39.8 2.05
dB Vp-p
2
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Integrated GPS Receiver and Synthesizer
AC ELECTRICAL CHARACTERISTICS (continued)
(MAX2740 EV kit, VCC = +3.0V, 50 system impedance, FRF = 1575.42MHz, FIF1 = 135.42MHz, FIF2 = 15.42MHz, FREF = 20MHz at 600mVpp, TA = +25C, unless otherwise noted.)
PARAMETER Synthesizer VCO Phase Noise Output Frequency for External GLONASS Tuner Magnitude GLS_OUT PFD Swing on Up and Down Outputs Rl = 500, Cl = 10pF Mag (UP-DOWN) CONDITIONS MIN TYP -91.5 90 300 250 MAX UNITS dBc/Hz MHz mVp-p mV VOLTAGE-CONTROLLED OSCILLATOR (VCO) (100kHz offset)
MAX2740
Note 1: Guaranteed by design and characterization. Note 2: Two tones at pin = -35dBm per tone, f1 = 1575MHz, f2 = 1576MHz. Note 3: Two tones at pin = -40dBm per tone, f1 = 1575MHz, f2 = 1576MHz.
Typical Operating Characteristics
(TA = +25C, unless otherwise noted.)
LNA GAIN vs. TEMPERATURE AND VCC
MAX2740-01 MAX2740-02
ICC vs. TEMPERATURE AND VCC
70 60 50 CURRENT (mA) 40 30 20 10 0 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 TEMPERATURE (C) VCC = 2.7V VCC = 3.0V VCC = 3.3V
20 18 16 14 GAIN (dB) 12 10 8 6 4 2 0 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 TEMPERATURE (C) VCC = 2.7V VCC = 3.0V VCC = 3.3V
RF MIXER GAIN vs. TEMPERATURE AND VCC
VCC = 3.3V 20 VCC = 3.0V GAIN (dB) 15 VCC = 2.7V
MAX2740-06
25
10
5
0 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 TEMPERATURE (C)
IF MIXER GAIN vs. TEMPERATURE AND VCC
MAX2740-03
VGA GAIN vs. VGC AND TEMPERATURE AT VCC = 3.0V
MAX2740-04
FGA GAIN vs. TEMPERATURE AND VCC
40 35 30 GAIN (dB) 25 20 15 VCC = 2.7V VCC = 3.3V VCC = 3.0V
MAX2740-05
40 35 30 GAIN (dB) 25 20 15 10 5 0 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 TEMPERATURE (C) VCC = 2.7V VCC = 3.3V VCC = 3.0V
30 20 10 VGA GAIN (dB) 0 -10 -20 -30 -40 -50 -60 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 AGC CONTROL VOLTAGE (V) TA = +25C TA = +85C TA = -40C
45
10 5 0 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 TEMPERATURE (C)
_______________________________________________________________________________________
3
Integrated GPS Receiver and Synthesizer MAX2740
Pin Description
PIN 1, 2, 4, 5, 6, 10, 11, 14, 15, 21, 22, 23, 26, 29, 32, 37, 41, 42, 47, paddle 3 7 8 9 12 13 16 17 18 19 20 24 25 27 28 30 31 33 34 35 36 38 39 40 NAME FUNCTION
GND
Ground. Connect pin to ground.
LNA_IN RFMIX_INGC VCC_ANA VCC_VCO TANK VCC_DIG DOWN UP GLS_OUT REF_IN FGA_OUTFGA_OUT+ FGA_INFGA_IN+ VGA_OUTVGA_OUT+ VGA_INVGA_IN+ IFMIX_OUTIFMIX_OUT+ IFMIX_INIFMIX_IN+ VCC_IFMIX
Input of LNA Circuit. Matching network and blocking capacitor required. Input to unused side of a differential pair that forms the RF section of a Gilbert cell mixer. This pin should be AC-grounded through 100pF. DC Control Voltage for Setting Gain Level of VGA. High input impedance. Voltage range of 0.5V to 2.5V. Supply Voltage Pin for Analog Circuits. This pin requires external decoupling of typically 0.01F. Supply Voltage Pin for VCO Circuit. This pin requires external decoupling of typically 1000pF. VCO Resonator Pin. A resonator is required at this pin. Supply Voltage Pin for Digital Section of the IC. This pin requires external decoupling of typically 0.01F. Down Output from the Phase-Frequency Detector. This pulses high whenever the phase of the VCO leads the phase of the reference. Up Output from the Phase-Frequency Detector. This pulses high whenever the phase of the VCO lags the phase of the reference. Output of Buffer that Provides a 90MHz Clock Signal. Requires external blocking capacitor. Reference Input for Synthesizer FGA Inverted Output. Blocking capacitor required. FGA Noninverted Output. Blocking capacitor required. FGA Inverted Input. Blocking capacitor required. FGA Noninverted Input. Blocking capacitor required. VGA Inverted Output. Blocking capacitor required. VGA Noninverted Output. Blocking capacitor required. VGA Inverted Input. Blocking capacitor required. VGA Noninverted Input. Blocking capacitor required. IF Mixer Inverted Output. Blocking capacitor required. IF Mixer Noninverted Output. Blocking capacitor required. IF Mixer Inverted Input. Blocking capacitor required. IF Mixer Noninverted Input. Blocking capacitor required. Supply Voltage Pin for IF Downconverter. This pin requires external decoupling of typically 1000pF.
4
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Integrated GPS Receiver and Synthesizer
Pin Description (continued)
PIN 43 44 45 46 48 NAME RFMIX_OUTRFMIX_OUT+ VCC_RFMIX RFMIX_IN LNA_OUT FUNCTION RF Mixer Inverted Input (same as RFMIX_OUT+) Open Emitter Output of the RF Downconverter. This pin requires an external pull-down resistor of 1.2k to establish the correct on-chip bias conditions. Requires a blocking capacitor. Supply Voltage Pin for RF Downconverter. This pin requires external decoupling of typically 100pF. Input to RF Mixer. Requires a blocking capacitor that may be used as part of the match network. LNA Output. Requires a pull-up inductor and a blocking capacitor. These may be configured as the matching network.
MAX2740
MAX2740
VCC
48
47
46
45
44
43
42
41
40
39
38
37 36 35 34 33 32 31 30 29 28 27 26 25
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
AGC GAIN SET
/2 /8
/6
/6 PFD
MAX4122
TO DSP
20MHz
MAX4122
Figure 1. Typical Application Circuit _______________________________________________________________________________________ 5
Integrated GPS Receiver and Synthesizer MAX2740
Applications Information
Figure 1 shows a typical application diagram in which the MAX2740 should be used. The RF front end consists of the antenna interface, MAX2740, two control loops (one for the AGC, the other for the synthesizer), and appropriate external components, including filters for image rejection and channel selectivity, operational amplifiers for the control loops, and resonator and tuning network for the VCO. Only the antenna input, an external 20MHz frequency reference, and an AGC input from the accompanying DSP are required. A differential output is provided from the MAX2740, which can be applied either to the external analog-to-digital conversion circuitry or directly to the companion DSP.
Variable-Gain Amplifier
This circuit compensates for receiver gain variation and unknown antenna cable losses. Under these conditions, the receiver will exhibit minimum implementation loss. The circuit has a useful gain control range of greater than 50dB, with a maximum gain level of 16dB.
Fixed-Gain Amplifier
This circuit has been designed to deliver 40dB of differential gain at the 2nd IF frequency of 15.42MHz. The differential inputs are received from the VGA outputs through a balanced lowpass filter circuit. The circuit's differential output is designed to drive a digitizer with a typical load impedance of 4k differential.
Voltage-Controlled Oscillator
The core of the L-band VCO is based on a commoncollector Colpitts topology. This circuit has been optimized for low thermal noise and high signal swing without asymmetrical clipping. The circuit is designed for use with a lumped inductor for low-cost applications. The self-resonance should be above 1440MHz so that parallel varactor tuning and the VCO internal capacitance produces resonance at 1440MHz.
Low-Noise Amplifier
This subcircuit requires input and output matching. The input match is typically a series capacitor, and the output is typically a shunt inductor to VCC and a series capacitor.
RF Mixer
The RF input is matched externally. The match consists of a series inductor and shunt capacitor. The source impedance for this circuit is the single-ended, 50 RF SAW used as an image reject filter. A second RF input is brought out to a separate pin for AC grounding. This ensures low ground impedance over a wide band and minimizes amplification of any noise at the IF frequency generated within the mixer structure. The IF output is delivered through low-output-impedance emitter followers and is suitable for directly driving a 135MHz IF SAW with a typical impedance of 400. The deliberate mismatch keeps the group delay distortion of the SAW within an acceptable level.
Synthesizer
The digital prescaler accepts the output from the oscillator's differential digital buffer and divides the frequency from 1.44GHz to 120MHz for the 2nd LO, 20MHz for the phase-frequency detector, and 90MHz for the GLONASS reference output. Divider blocks are arranged to ensure that the 2nd LO drive has minimum duty cycle distortion. A simple output buffer is used to deliver the GLONASS reference signal to a typical external load impedance of 500. The phase-frequency detector is a classical dual flipflop with ANDed feedback to a reset function. UP and DOWN outputs are provided through emitter follower buffers. These outputs deliver pulse-width-modulated signals that in phase-acquisition mode give a phase detector range of 2. With the PLL not in lock, either the UP or DOWN output will be active and drive the VCO frequency toward the reference frequency. The phase detector outputs feed directly into an active, lead-lag differential loop filter.
IF Mixer
The IF downconverter receives the differential 1st IF of 135.42MHz from the SAW and delivers a differential 2nd IF signal at 15.42MHz. The circuit has been optimized to deliver a high level of conversion gain with adequate IIP3 and noise figure. The circuit is terminated on the input with a differential 100 to establish the correct embedding impedance for the IF SAW. The emitter follower outputs drive directly into a high-impedance, differential, three-pole lowpass discrete lumped element filter.
6
_______________________________________________________________________________________
Integrated GPS Receiver and Synthesizer
Package Information
48L,TQFP.EPS
MAX2740
_______________________________________________________________________________________
7
Integrated GPS Receiver and Synthesizer MAX2740
NOTES
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.
8 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2000 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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