MAX2769 GPS Reference Design

Abstract: This reference design is a complete RF front-end solution for a GPS receiver using Maxim's MAX2769 GPS receiver chip. The MAX2769 is a low cost, single conversion, low IF GPS receiver that offers two integrated LNAs with different specifications, I/Q channel filters with variable bandwidth and order, and a digital IF output that supports 1-bit and 2-bit operation. This reference design offers high performance, small size, and low BOM cost.

Figure 1. GPS reference design features the MAX2769.
Figure 1. GPS reference design features the MAX2769.

Important Design Features

  • Dual-Input Uncommitted LNA for Separate Passive and Active Antenna Inputs
  • Integrated Active Antenna Sensor Which Can Autoswitch the Antenna Input
  • The I and Q Channel-Select Filters Can Be Selected as Either Third or Fifth Order
  • Provides 110dB Cascaded Gain and a 1.5dB Cascaded NF in LNA1 Mode
  • The IF Output Is Adjustable in 63 Steps Between 0MHz and 12.5MHz
  • Can Be Used in Preconfigured States that Do not Require Programming Through the 3-wire SPI™ Interface

Figure 2. Block diagram for the GPS reference design.
Figure 2. Block diagram for the GPS reference design.

Lab Measurements

Supply Current Summary

VCC = +3.0V, TA = +25°C
Parameter Test Conditions Meas. Unit
Operating Supply Current Using LNA1 in default and low-current modes 18 mA

Receive Summary

Operating conditions: VCC = 3V; TA = +25°C, Operating in default mode, PCB trace losses are included.
Parameter Test Condition Meas. Unit
LNA1 Power Gain Default and low-current modes 18.6 dB
LNA1 Noise Figure Default and low-current modes 1.05 dB
LNA1 Third-Order Input Intercept Point Default and low-current modes; LNA input to output. P1 = P2 = -30dBm; f1 = 1575MHz, f2 = 1576MHz -1 dBm
LNA2 Power Gain Default mode 12.9 dB
LNA2 Noise Figure Default mode 1.35 dB
LNA2 Third-Order Input Intercept Point Default mode -2 dBm
Overall System NF Using LNA1; PGA gain is maximum (CONF3[27:22] is 111111) 1.6 dB
Using LNA2; PGA gain is maximum (CONF3[27:22] is 111111) 3.1
IF Out Freq/Gain Range Through System Using LNA1 1575.42MHz in, 4.092MHz out; analog output mode 59 -117 dB
4MHz Offset Rejection 1579.42MHz in, third-order BPF; PGA gain is maximum (CONF3[27:22] is 111111) 32 dB
1579.42MHz in, fifth-order BPF; PGA gain is maximum (CONF3[27:22] is 111111) 51
IF Passband 3dB Bandwidth IF filter center bandwidth 2.6MHz; set bit 4:3 of CONF1 register to 00 2.9 MHz

Operating Characteristics

Figure 3. ACPR performance at Tx power = 15.7dBm, EVM < 5.6%.
Figure 3. Input S11 of the MAX2769 LNA1. Measured by network analyzer at 1575.42MHz. The S11 is -10.4dB.

Detailed Description

This reference design is a low-cost, single-conversion, low-IF GPS receiver. The design offers more flexibility and performance than its predecessors for a wide range of GPS applications such as mobile handsets, PDA's, embedded PCs, and automotive applications.

Related Parts
MAX2769 Universal GPS Receiver Samples  

Next Steps
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© Sep 22, 2008, Maxim Integrated Products, Inc.
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APP 4279: Sep 22, 2008
REFERENCE SCHEMATIC 4279, AN4279, AN 4279, APP4279, Appnote4279, Appnote 4279