MAX2769 GPS Reference Design

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

Lab Measurements

Supply Current Summary

V_CC= +3.0V, T_A= +25°C


Parameter	Test Conditions	Measurement	Unit
Operating Supply Current	Using LNA1 in Default and Low-Current Modes	18	mA

Receive Summary

Operating conditions: V_CC= 3V; T_A= +25°C, Operating in default mode, PCB trace losses are included.


Parameter	Test Condition	Measurement	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= 1567MHz	-1	dBm
LNA2 Power Gain	Default Mode	12.9	dB
LNA2 Noise Figure	Default Mode	-2	dBm
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
Overall System NF	Using LNA2; PGA Gain is Maximum (CONF3[27:22] is 111111)	3.1	dB
IF Out Freq/Gain Range Thru 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
4MHz Offset Rejection	1579.42MHz in, fifth-order BPF; PGA Gain is Maximum (CONF3[27:22] is 111111)	51	dB
IF Passband 3dB Bandwidth	IF Filter Center Bandwidth 2.6MHz; Set Bit 4:3 of CONF1 Register to 00	2.9	MHz
LNA1 Third-Order Input Intercept Point	Default and Low-Current Modes; LNA Input to Output. P1 = P2 = -30dBm; f1 = 1575MHz, f2 = 1567MHz	-1	dBm

Operating Characteristics

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.