Positioning is an increasingly important part of an embedded design as more and more devices become mobile. Adding this capability into equipment that has to be smaller, lighter and have longer battery life is a major challenge. At the same time there are the challenges of implementing an effective wireless design with high performance and low power, while meeting the requirements of the project timeline and the certification authorities.
These challenges are being addressed by a new generation of wireless modules that are using the latest miniaturization technologies to make use of the various global positioning systems (GPS) around the world, with the footprint of GPS modules falling dramatically over the last few years.
GPS has several varieties, from the US GPS, Europe's Galileo, Russia's GLONASS and the Chinese Beidou systems. Modern wireless chipsets from a wide range of suppliers provide access to all these satellite systems, and advances in silicon manufacturing technology provide access to all these systems.
However, these devices still have to be integrated into a design and there are key components such as SAW filters that cannot be integrated into the silicon, and therefore provide a limit to the amount of miniaturization that is possible purely from silicon.
The integration of the silicon devices can help reduce the power consumption, although there are challenges of RF and digital integration that means the most advanced process technology is not appropriate. There are also issues of static current leakage that increase the power and the handling of noise in the system which can mean more power is required to get the required performance. Higher power consumption means more heat generated and larger batteries required; both of which limit the amount of miniaturization that is possible.
This is critical as the use of GPS modules for applications such as the Internet of Things (IoT) can be dependent on a small tag that tracks high-value items around the world – the smaller the tag, the more effective the tracking system can be. That system may also have to run for years off a tiny cell battery, making the power consumption a critical element in both size and performance.
Similarly for wearable systems, customers are requiring that the end systems are inconspicuous and non-intrusive, driving designs to be as small and power efficient as possible.
While the perceived wisdom is that the optimal implementation of a GPS design is a custom implementation on a board, module makers are allowing more technology to be integrated into a small package that not only reduces the overall footprint, but they are also providing pre-certified components to reduce the compliance time of the project and reduce the time to market.
Being able to use chip-scale packaging for the receiver and the power management chips and integrate other passive devices into a substrate that is optimized for the power consumption allows the system designer to use lower cost two-layer printed circuit boards that can be easily manufactured, rather than a complex custom design that pushes the tolerance of the manufacturing process.
This is a key issue in the production of such boards that are pushing the limits of miniaturization. To get the smallest design with a custom layout, chip-scale ICs and discrete components mean pushing the limits of the manufacturing tolerances, increasing the risk of problems with the units and reducing the yield. Reducing the guard tolerances also has a bigger effect on the RF front-end, potentially increasing the noise and hitting the overall performance.
Telit is a key provider of machine-to-machine systems and so has applied the latest miniaturization technologies to its latest GPS modules.
The Jupiter JF2 measures 11 x 11 x 2.6 mm in a 32-pin pad QFN (Quad-Flat No-leads) package and weighs just 1 gram for integrating into systems where weight is a challenge. The heart of the JF2 is the SiRFstarIV integrated silicon receiver that is combined with other key components.
One of the key advantages of the module is that it can be seamlessly integrated with Telit's cellular and short-range wireless modules to provide a flexible solution for machine-to-machine (M2M) and Internet of things (IoT) designs. The 1.8 V supply and low-power modes allow it to be used in applications from fleet monitoring to battery-powered fitness designs.
Figure 1: Telit's Jupiter JF2 module measures 11 x 11 x 2.6 mm.
Despite the small size, the module has been optimized to provide sensitivity stability particularly at the extremes of -40 and 85°C, maintaining the performance down to -147 dBm in acquisition and -163 dBm in tracking the satellite signals. It also provides one-satellite acquisition of the UTC time signal alongside the 48-channel signal acquisition and digital signal processing.
One of the key elements of a miniature GPS design is how quickly it can get a fix on the satellites. The JF2 has several stand-by modes, from TricklePower, Push-To-Fix, and Micro Power that are designed to meet different requirements for the interval between position updates and for power consumption. All of these modes are similar but provide different output rates and reliability, from 14 μA in hibernation mode to 10 mA in tracking mode.
The module also has TricklePower duty cycling mode with a user-selectable position update interval, providing high-quality GPS accuracy and dynamic motion response at a reduced average current draw. A Push-to-Fix mode provides infrequent periodic position updates and also allows position requests from the user with short time to first fix (TTFF). The Micro Power mode keeps the receiver in Hot Start conditions while maximizing the time spent in a very-low-power state.
Integrating a module has to be as simple as possible, and the JF2 has a single 1.8 V supply with fail safe I/O including RTC and TCXO inputs and host I²C, SPI and UART support, as well as optional SPI Flash or Serial EEPROM external memory and can be mounted on a cost effective two-layer circuit board.
The FGPMMOPA6H from Embedded Artists uses MediaTek's MT3339 GPS chipset that has a sensitivity of -165 dBm and an instant Time-to-First Fix (TTFF) with low power consumption for precise GPS signal processing.
Figure 2: The FGPMMOPA6H module from Embedded Artists.
The 3.3 V 15 x 15 mm module is aimed at handheld devices such as tablet PCs, as well as M2M applications and asset management and tracking and uses a POT (Patch On Top) architecture. This places the microstrip antenna on top of the ceramic module for a compact solution, but the module also adds extra external antenna I/O. To help get the best performance and the lowest power and to support the smallest footprint, the module also has an automatic antenna switching function, short-circuit protection and an 'Antenna Advisor' that helps with the detection and notification of different antenna statuses, including active antenna connection, antenna open circuit and antenna shortage.
Up to twelve multi-tone active interference canceller options provide more flexibility in the system design, and the module supports up to 210 channels - 66 for search and 22 simultaneous tracking channels.
All this contributes to an acquisition power consumption of 82 mW, with 66 mW for tracking.
Taiyo Yuden's 3.3 V GYSFFMAXX GPS module similarly uses a MediaTek GPS receiver, the MT3329, and integrates the crystal, oscillator, SAW filter and low noise amplifier to miniaturize the system to a footprint of 10.8 x 10 mm with 2 mm high metal shielding.
Figure 3: Taiyo Yuden's metal-shielded GYSFFMAXX GPS module.
Some modules are also designed to make the prototyping easier. If you already use the MikroBus board system from Mikroelektronika then there is a GPS module that can be used. The GPS Click accessory board uses the 17 x 22 mm LEA-6S u-blox 6 module and is powered by a 3.3 V supply. The board can be interfaced with a microcontroller through UART or I2C, or data can be acquired using PC application through USB connection.
Figure 4: Using the LEA-6S GPS module in the MikroBus prototyping system.
Conclusion
The footprint of GPS modules has been falling in size as the demand for miniaturization increases in M2M and IoT designs. Moving from the 17 x 22 mm module down to 10 x 10 mm and now 5 x 5 mm is a result of increasing integration in silicon and a reduction of voltage.
Moving to the smaller modules has required more focus on noise and power management, but is allowing system designers with limited RF experience to add positioning functionality quickly and easily in conditions where space is at a premium. Integrating the SAW filter, amplifiers and even the patch antennas is now possible without increasing the complexity of the manufacturing process, using the modules to maintain simple two-layer board designs and to reduce the time taken for regulatory compliance.
