RF IC Building Block Solutions for GPS


Maxim's family of high performance CMOS and Silicon Germanium (SiGe) building block RF ICs for implementing an GPS RF-to-IF receiver are described.

Additional Information:

There are many commercially available IF-to-baseband IC solutions for GPS Applications, and many companies have opted to design their own proprietary ASICs, but lack an RF-to-IF front end for downconverting the transmitted GPS frequency to a low-IF frequency. Maxim has produced several RF ICs that have proved an excellent choice for accomplishing these tasks.

The MAX2741/MAX2742/MAX2745 are a family of high-performance CMOS single-chip GPS front-end downconverters. These state-of-the-art devices consume extremely lowpower and do not need the costly IF SAW filters or bulky discrete IF bandpass filters.All devices are fully equipped with a low-noise amplifier, mixer, BPF, automatic gain control amplifier, local oscillator synthesizer, clock buffer, and digital sampler. The selector guide for these products are shown in Table 1. For more information on these products, visit the links below for data sheets and application notes.

Table 1. CMOS GPS RF Front-End Receiver IC Selector Guide

Part Supply Voltage (V) Supply Current (mA) Reference Clock (MHz) IF Frequency (MHz) Conversion Gain (dB) Noise Figure (dB) IIP3 (dBm)
MAX2741 2.7 to 3.0 30 2 to 26 37.38 (first)
3.78 (second)
32 (first)
47 (second)
4.7 (first)
12 (second)
-30 (first)
-36 (second)
MAX2742 2.4 to 3.6 14 18.414 1.023 117 4.5 -32
MAX2745 2.4 to 3.6 21 16.368
4.092 120 3.5 -25

The MAX2654/MAX2655 SiGe LNAs offer high gain, low noise, and high linearity at 1575MHz. Both RF ICs incorporate 50Ω output-matching networks for reduced component count. The MAX2654 RF IC delivers 15.1dB of gain, a noise figure of 1.5dB, and an input third-order intercept point (IIP3) of -7.8dBm. For improved linearity, the MAX2655 RF IC offers 14.1dB of gain, a noise figure of 1.45dB, and an adjustable IIP3 performance of +2.2dBm to +3.8dBm. The supply current for the MAX2654 is a low 5.8mA, whereas the supply current for the MAX2655 is adjustable from 5.9mA to 10.1mA. Both devices also feature a 0.1µA low-power shutdown mode. The MAX2641 SiGe LNA is another excellent choice, offering 15.7dB of gain, an extremely low noise figure of 1.2dB at 1575MHz, and an IIP3 of +1.4dBm. The supply-current draw is a low 3.5mA. The MAX2641 does not offer a low-power shutdown mode or an integrated output-matching network.

Maxim currently does not offer a stand-alone GPS LNA that supports gain-step, but retuning the MAX2563 to the GPS band offers an excellent solution. The MAX2563 is a SiGe LNA designed to operate in the US PCS and European DCS receive bands. After replacing the matching components, the MAX2563 delivers 19.2dB of gain, 1.57dB of noise figure, and -5.2dBm of IIP3. For more information, please see application note 3248, "MAX2653 LNA with Gain-Step, Retuned for GPS Applications."

The MAX2680/MAX2681/MAX2682 are a family of Silicon Germanium downconverting mixers that accept RF frequencies in the range of 2.5GHz to 400MHz, which makes it outstanding for GPS Applications at 1575MHz. The IF output can be tuned for IF frequencies between 10MHz and 500MHz. See Table 2 below for the performance of the MAX2680, MAX2681, and MAX2682.

Table 2. GPS Silicon Germanium (SiGe) Downconverter IC Selector Guide

Part Supply Current (mA)
IIP3 (dBm)
NF (dB)
Gain (dB)
IIP3 (dBm)
NF (dB)
Gain (dB)
MAX2680 5.0 -12.9 6.3 11.6 -8.2 8.3 7.6
MAX2681 8.7 -6.1 7.0 14.2 +0.5 11.1 8.4
MAX2682 15.0 -1.8 6.5 14.7 +4.4 10.2 10.4

The following block diagram summarizes the important features of the Maxim's various building-block GPS RF ICs.

RF ICs for GPS Receivers
RF ICs for GPS Receivers