Keywords: GPS receiver, MAX2769, RF
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REFERENCE DESIGN 4279  INCLUDES: Tested Circuit Board Available Description Test Data 

MAX2769 GPS Reference Design

Sep 22, 2008

 
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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.

Click here for an overview of the wireless components used in a typical radio transceiver.
Click here for an overview of the wireless components used in a typical radio transceiver.


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 Free Samples  


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APP 4279: Sep 22, 2008
REFERENCE DESIGN 4279, AN4279, AN 4279, APP4279, Appnote4279, Appnote 4279

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