GPS/GNSS receiver-modules are an increasingly popular option amongst product designers. They offer near-instantaneous access to location and timing data, without the need to select, design and integrate an antenna, module, filters, and other RF components on a circuit board. It’s a much easier option, offering a drop-in solution for connectivity to incredibly weak signals.
Although these solutions offer exceptional ease of integration, there are still some things to consider to ensure a device performs well. For starters, you will want to consider which module is right for your device.
Selecting the right module
Choosing the right module for a given design is critical. However, it is important to make this decision early on in the design process.
The signals propagated from satellites are much weaker than wireless signals from WLAN or even cellular technologies, by up to hundreds of times. Without a strong, reliable connection, the accuracy of GPS may be impaired, rendering the function less useful to consumers.
To maximise the performance of a module, selecting one early will enable the designer to create an optimised environment for GNSS/GPS signals. As the design progresses, the level of flexibility afforded to a designer over the integration of a module diminishes.
There is a wide variety of configurations for GPS/GNSS modules. Some of these are complete receiver-modules, containing an antenna, RF circuitry, BB, and some even containing SAW filters.
Conversely, there are modules that enable designers to connect an external antenna, which can boost the performance of a GPS system by harnessing an antenna capable of delivering higher levels of performance.
Ant + RF + BB
Ant + RF + BB
RF + BB
RF + BB
Antenna + RF
Antenna + RF
This variety enables designers to select the most appropriate solution to their device. Commonly, modules without antennas are used in automotive applications, as the size of the vehicle overall is capable of harnessing an external antenna. Whereas in smaller devices, modules with built-in antennas are the most compact all-in-one solutions.
Receiver-modules rely heavily on their placement in order to perform well. These typically perform best when placed in a predetermined position on the circuit board – as specified within the data sheet or product specification for the GPS/GNSS receiver-module. The design of the receiver-module will dictate how to position the module for maximum performance.
Much like a GNSS/GPS antenna, the optimum placement is typically along the longest edge of the PCB, in the centre. This affords designers some extra flexibility in terms of integration, as ceramic patch alternatives need to be placed centrally on a circuit board in order to perform well.
Although Antenova’s RADIONOVA range of receiver-modules perform well when placed along the centre of the longest PCB edge, there is an allowable offset. This can help further clear the centre of the PCB for high-speed digital ICs.
Ground plane clearance
Antennas are being manufactured in smaller and smaller form factors. However, these antennas still need to comply with the laws of physics in order to function well. To do this, many antennas utilise a ground plane.
To ensure high levels of performance, the keep out areas should also be respected. This means keeping the module clear from metallic objects, components, screens, batteries or any other moving component.
Tuning enables a module to perform well in its operating environment. This enables the integrated antenna to perform well with minimal battery consumption and maximum accuracy. It also counteracts the performance degradation due to he product housing or any other nearby components that could detune the antenna.
To tune a module to the operating frequency, you can use a network analyzer and adjust each of the on-board components to achieve the desired resonance. For more information about tuning, download our guide to matching and tuning.
RADIONOVA modules feature an array of pins for drop-in integration. For a description of the pin roles, see the corresponding product specification. From this information, you can quickly and easily configure your module to function. Some pins have multiple functions.
Not achieving a fix?
The most frequent reason why a module is unable to achieve a fix is due to the lack of tuning and matching. In order to do this, review the reference design of the module in the corresponding data sheet. If the module is integrated in this way, it should function even with the stock matching components.
Firstly, make sure that you are connecting the module with respect to the guidelines stipulated in the datasheet. One of the most common errors is where traces run underneath the module, which generate noise. Also, make sure that both Vcc and Vbackup pins are connected, otherwise the module will not function.
If the module is implemented correctly, then you can proceed to test the communication. The quickest way to do this is by using the test command: $PMTK000*32.
The test command should return PMTK001,0,3 (ACK OK). After testing the communications, wire it up on a PCB. Ensure that the antenna is correctly tuned and it corresponds to the reference.
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