GPS Receiver Module Fundamentals

This page provides a foundational overview of GPS receiver modules. It covers the basics, including an application note and a list of GPS module manufacturers. As we know, a GPS device contains a GPS receiver that obtains position information from GPS satellites.

The position data includes latitude, longitude, and altitude coordinates. A Low Noise Block Converter (LNB) and other modules/subsystems are typically required, as shown in the figure below, to recover the signal-to-noise ratio (S/N) above a certain threshold. This is necessary for recovering error-free data from the received carrier-to-noise ratio (C/N).

GPS Receiver Block Diagram

Refer to the GPS transmitter section (the GPS satellites orbiting in space).

To recover the baseband information from the received GPS signal, a Costas loop is used with a phase-synchronized local oscillator (LO); otherwise, the signal cannot be reliably detected.

The required Pseudo-Noise (PN) code is locally generated to detect the chip of the spread spectrum signal received. The number of correlators depends on the number of visible GPS satellites in the sky. Most GPS receivers have 12 correlators.

LNB stands for Low Noise Block Converter, which is a combination of both a Low-Noise Amplifier (LNA) and an RF converter.

Software running on the CPU is used to calculate X, Y, and Z coordinates, which in turn are used to calculate latitude, longitude, and altitude.

GPS Receiver Measurements

GPS receivers perform two key measurements using received GPS signals:

• Pseudo-range Measurement: The received C/A code or P code is compared with a locally generated code using a lookup table. This determines the time delay between the GPS satellite and the GPS receiver. This measurement is called pseudo-range.

• Carrier Phase Measurement: This method obtains the phase difference between the received carrier signal and a locally generated signal at the same frequency. This technique offers millimeter-level precision. However, it’s less accurate because it assumes the received and local carriers are locked and some prior phase information is known at the receiver (which isn’t always true).

GPS Module Manufacturers

Here’s a list of manufacturers of GPS modules, GPS receivers, and related components:

• Broadcom
• Futurlec
• Furuno Electric Co.
• Sparkfun Electronics
• Maxim Integrated
• Navsync
• Skyworks Solutions, Inc.
• Central Electronics Ltd.
• SkyTraq Technology, Inc. (Taiwan)