Avago ALM-1812高增益GPS前端方案

Avago公司的ALM-1812是高增益低噪音GPS前端放大器,组合了高增益LNA和GPS FBAR滤波器.LNA采用Avago的GaAs增强模式pHEMT工艺,而一流的FBAR滤波器在Cell/PCS频段有极好的抑制特性,大于85dB. ALM-1812的增益为19.1dB,NF为1.66dB,IIP3 = +2 dBm, IP1dB = -8 dBm.本文介绍了ALM-1812主要特性和指标, 应用电路,演示板布局和电路图以及所用元器件与散射参数和测试参考平面图.

ALM-1812: High-Gain GPS Low Noise Amplifier with Integrated Filters and Variable Current/Shutdown Function

Avago Technologies’ ALM-1812 is a GPS front-end module that combines a high-gain low-noise amplifier (LNA) with GPS FBAR filters. The LNA uses Avago Technologies’ pro­prietary GaAs Enhancement-mode pHEMT process to achieve high gain with very low noise figure and high linearity. Noise figure distribution is very tightly controlled. A CMOS-compatible shutdown pin is included either for turning the LNA on/off, or for current adjustment. The integrated filter utilizes an Avago Technologies’ leading-edge FBAR filter for exceptional rejection at Cell/PCS-Band frequencies.

The low noise figure and high gain, coupled with low current consumption make it suitable for use in critical low-power GPS applications or during low-battery situations.

ALM-1812主要特性:

• Very Low Noise Figure

• Exceptional Cell/PCS-Band rejection

• Low external component count

• Fully-matched at RF input and RF output

• Shutdown current: < 1 uA

• CMOS compatible shutdown pin (SD)

• ESD:> 3kV at RFin pin

• 4.5 x 2.2 x 0.95 mm3 size

• Adjustable bias current via single external resistor/voltage

• Lead-free, Halogen free and meets MSL3

ALM-1812主要指标:

Specifications (Typical performance @ 25°C) At 1.575GHz, Vdd = 2.8V, Idd = 6.8mA

• Gain = 19.1 dB

• NF = 1.66 dB

• IIP3 = +2 dBm, IP1dB = -8 dBm

• S11 = -10 dB, S22 = -15 dB

• Cell-Band Rejection:> 90dBc

• PCS-Band Rejection:> 85dBc

ALM-1812应用:

• GPS Front-end Module

图1. ALM-1812应用电路

图2.ALM-1812演示板布局图

应用电路所用元件表:

图3.ALM-1812演示板和应用电路框图

Notes

1. The module is fully matched at the input and output RF pins. The RFin pin is directly connected to a shunt inductor that is grounded. The RF output filter blocks DC. Best noise performance is obtained using high-Q wirewound inductors. This circuit demonstrates that low noise figures are obtainable with standard 0402 chip inductors.

2. C2 and L2 form a matching network that affects the frequency response and linearity of the LNA, these can be tuned to optimize gain and return loss.

3. L1 and R1 isolates the demoboard from external disturbances during measurement. It is not needed in actual application. Likewise, C1 and C3 mitigate the effect of external noise pickup on the Vdd and Vsd lines respectively. These components are not required in actual operation.

4. Bias control is achieved by either varying the Vsd voltage with/ without R2, or fixing the Vsd voltage to Vdd and adjusting R2 for the desired current.

图4.ALM-1812散射参数和测试参考平面图