MAX2769 GPS Reference Design
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 1. GPS reference design features the MAX2769.
详情介绍
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
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. 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.