"GPS technology is increasingly combined with low power mode, that is, these miniature devices can now be powered by solar cells. For example, a company that is from the United States, Australia, United Kingdom and China, forms a named Retrievor The consortium is fundraising through the form of a population to develop a coin-sized GPS tracking device. Small self-powered GPS systems use Android or Apple iOS app to provide location information, which can be used to track valuables, even pets.
The RETRIEVOR device has a diameter of 28 mm (1.10 "), 10 mm (0.39") and integrated an antenna in the module to reduce its own volume. The device uses a Sirfstariv GPS processor, which can be used in a variety of challenge GPS environments such as indoor tracing, or for end users move. This high-level GPS performance source has a new GPS firmware that detects around the surrounding environment, temperature, satellite signals, and updating internal data in any possible case, thereby providing a few short continuous navigation functions.
The power required by the Retrievor receiver comes from an integrated solar panel and a mobile charger that supplies power to a 3.7 V lithium ion battery or charged by miniature USB. User-defined ping rates can be adjusted once every second, so Retrievor may never be charged.
Build a GPS receiver
A high-level compact module of RF and antennas can be combined with the energy collection transmitter, the power manager, form a similar small system independent of the power supply. After careful considering the system power budget, solar cells (such as Sany's products) can meet all power requirements. In these small volumes, it is also critical to avoiding the various problems brought about RF layout, otherwise power consumption will increase the energy collection source.
M10478 from Antenova, is a highly integrated GPS RF antenna module for L1 band GPS and A-GPS systems. The device is used in the same Sirfstariv GPS architecture as the Retrievor receiver, and an antenova high energy antenna technology is intended to provide an optimum radiation map suitable for GPS reception.
All front end and receiver elements are placed in a single package laminated substrate module to form a complete GPS module that meets the best performance requirements. M10478 uses a single 1.8 V positive power supply, which has a lower power consumption and has a variety of low power modes that can further save energy, so it can be powered by a solar cell power supply type 3.7 V lithium ion battery. Accurate 0.5 PPM TCXO ensures that mobile applications have a short first positioning time (TTFF); this module is supported by independent software support, compatible with UART, SPI, and I2C master interfaces.
Trickle power supply (TP)
This module has a "trickle power" operating mode that reduces power and realizes collecting source. This module can enter the duty cycle mode to reduce the average current power consumption, but still maintain high sensitivity, high performance to ensure that it receives a weak signal.
Under normal conditions, the module is generally full of power in TP mode 100 - 900 ms and is positioned once, and then entering a lower power-consuming manner that lasts 1 - 10 S. Sometimes (usually per 1800 s), the module will re-enter the full power mode update the epicardial data.
In TP mode, if the signal condition is bad (less than 30 dB-Hz), the module will automatically switch to the power mode to enhance the navigation performance, and enter the TP mode again when the signal condition returns to normal. This will form a variable power-saving state, but for a fixed output rate, a more reliable performance can be obtained. When using TP mode, it is similar to the application with full power mode, but it will significantly reduce power consumption under strong signal conditions.
As for the design of an antenna, the SG series GPS receiver module (Linx Technologies product) is a self-holding high-performance GPS receiver using onboard LNA and SAW filters. This device is based on the Sirfstar III chipset, with high sensitivity and low power consumption, which helps to maximize the running time of energy collection applications. The SG series has more than 200,000 active correlators, even in a few seconds of the minimum signal level and track up to 20 satellites.
The receiver uses a compact SMD package compatible with reflow weld without programming or increasing RF components (except antennas), can form a complete GPS solution. Five GPIOs can be easily configured by simple serial commands, coupled with the standard NMEA data output of the module, even if the engineers who have previously no RF or GPS experience can be easily integrated. GPS kernel can automatically process all necessary initialization, tracking, and computing tasks without programming. The RF part is optimized for a low level signal, so any type of device does not require adjustment when producing.
By default, the SG series is full of power mode, but also built-in power control mode, this mode is called adaptive trickle power mode when adopting energy collection sources.
Antenna consideration
The SG series can use a wide variety of external antennas. This module provides adjustment power output to simplify the use of GPS antennas, but require external power. This brings great flexibility to the designer, but in order to ensure optimum performance, it must be carefully selected.
Miniature portable devices can be used in each variation direction, and therefore, better overall performance can be achieved compared to high gain and a narrower antenna element, a widely beam and uniform antenna element can achieve better overall performance. Conversely, for an antenna adopting a fixed installation and the foreseeable antenna, if its shape and gain characteristics are suitable for the target application, it helps to play antenna performance. Evaluate multiple antenna solutions in the actual solution, which is a good way to quickly determine which antenna is most satisfied with application requirements.
When used for GPS, the antenna should have a good right-rotation polarization (RHCP) to match the GPS signal polarization. Ceramic sheet antennas are the most common antenna type, with many different shapes, sizes, and styles. The passive antenna is only a antenna tuning to the correct frequency, and the active antenna increases a low noise amplifier (LNA) before and after the module, it is used to enlarge the micro GPS satellite signal, but power consumption should exceed energy. The supply of the source is supplied because the VOUT line provides 2.85 V voltage to the external LNA at 30 mA.
Keep a 50 Ω path between the antenna and modules is extremely critical because the error in the layout may significantly affect the module performance. Although the design of this module makes it easy to integrate, pay special attention to the layout of PCB, this is important. If a good layout technology cannot be used, the module performance will be greatly weakened, causing the chip to increase power consumption when compensating for lower performance.
The main purpose of the layout is to maintain a stable 50 Ω feature impedance from the entire path of the antenna to the module. The module should be reasonably isolated from other components on the PCB, especially with high frequency circuits such as crystal oscillators, switching power supplies, high speed bus, such that RF and digital circuits are located in different regions on the PCB.
PCB printing line should not cross the module, it is important, otherwise it will cause a lot of trouble when designing such a small system. There should be no copper wire or print line on the PCB layer in the module or below the module, that is, the bare plate state is maintained. There is a printed line below the module to cause short circuit or coupling of printing lines on the product board.
Place a large continuous ground layer in the next layer opposite to the module to form a low impedance return path for grounding and maintaining stable strip line performance. The printed line should be as short as possible, and it will be greatly helpful under the module or any other component, since the inductance is increased by using through the through holes to printed on the plurality of PCB layers. Instead, the plurality of through holes should be used to ground the ground plane and the component.
For small designs, the product is typically sealed, which can be used in various types of pottings having different electrical properties. Because such pottings can seriously affect RF performance and product rework or maintenance, designers should choose to find qualified materials.
Power management
When the RF portion and the GPS primary core, the module can obtain a power supply from a backup battery powered by the SRAM memory and the RTC. In this way, the module can have a faster TTFF before the power is restored. The memory and clock current consume about 10 μA, so it is feasible to use solar cells as a power source.
This also means that small lithium ion batteries are sufficient to provide power for these functional parts. This will greatly reduce power consumption, extend the service life of the main battery, and quickly position when the module power is restored. One of the problems related to energy collection is that modules require a clean, voltage regulator performance, noise is less than 20 mV, as power supply noise will seriously affect the receiver sensitivity.
For example, an LTCR3108 device (Linear Technology), which is a highly integrated DC / DC converter and manages excess electrical energy from extremely low input voltage sources for collected. In this way, electrical energy can be acquired from a small solar cell for a coin size GPS receiver because this boost topology can operate at an input voltage as low as 20 mV.
The LTC 3108 has a minimum input resistance (load) between 2 Ω to 10 Ω, which is specifically determined by the input voltage. When the input voltage is lowered, the input resistance is increased, so the LTC 3108 can optimize the power transmission of the power supply with several ohmic sodes. When providing higher input voltages in the case, lower source resistors always achieve greater output current capabilities.
This feature can be achieved in a mature architecture to add a unique VOUT option. The 2.2 V LDO powers to the external processor, while the main output is programmed as one of the four fixed voltages after programming, and powered by the GPS receiver.
The LTC3108 can also manage the charging and adjustment of multiple outputs in a system whose average power consumption is low, but the GPS receiver generates a higher periodic load current when the GPS receiver is in position polling. The power manager uses an external boost transformer based on a MOSFET switch, a small coupling capacitor constitutes a resonant rose oscillator. In this way, the power manager can boost the minimum 20 MV input voltage to a sufficiently high level to provide multi-channel regulated output to power to other circuits. The oscillation frequency is determined by the inductance of the secondary winding of the transformer, and is usually 10 kHz to 100 kHz.
Programmable output
The main output voltage VOUT is charged by the VAUX power supply, and the user can program the voltage to the voltage by voltage selection pin VS1, and VS2 makes it a line in four regulations. Although the typical value of the threshold logic voltage of VS1 and VS2 is 0.85 V, it is recommended to ground it or connected to VAUX.
When the output voltage is slightly lower to the voltage regulation value, charging current can be generated as long as VAUX is greater than 2.5 V. Once VOUT reaches a suitable value, the charging current is cut off. VOUT is set by the internal programmable resistor driver, so there is no need to have a large external resistor, and this external resistor is easily affected by the disclosure and power consumption.
Power monitoring
The power supply is also used to monitor voltage Vout. This is an open drain output with a weak pull-up resistor (1 MΩ) that reaches the LDO voltage; the output will rise within 7.5% of VOUT to be charged to its regulated value. If VOUT drops more than 9%, the PGOOD will be lowered to signal the microprocessor; PGOOD is used to drive the chip I / O instead of driving a large current load such as LEDs. The PGOOD signal can also be used to wake up a microprocessor or other circuit in a sleep state when Vout reaches a regulated value.
Vout2 can be turned on and turned off by the host through the VOUT2_EN pin. When Vout2 is enabled, it is connected to VOUT through a 1.3 Ω P-channel MOSFET switch. This output by the main processor can be used to power the external circuit, such as a sensor without low power dormancy or shutdown function, amplifier.
The decoupling capacitors on VOUT2 can minimize, which can make it more quickly, and then shorten the burst time, and the smaller duty cycle can be achieved in the pulse application of the wireless sensor and the transmitter. Small VOUT2 capacitors can also minimize electric energy in the charging process in the capacitance each time Vout2. Vout2 has a soft start time of approximately 5 μs to limit the charging current and minimizes the burrs of the main output while Vout2 is enabled. In addition, there is a current limiting circuit that can reduce peak current to 0.3 a (typical). VOUT2 enables typical thresholds to be entered to 1 V, lag is 100 mV, so it can be compatible with logic circuitry.
GPS special chip
Another option is a GPS special chip, not a module. The total voltage gain of the MAX2741 L1 band GPS receiver IC is 80 dB, and the cascaded noise coefficient is 4.7 dB, which can reach the receiver sensitivity in various applications for the indoor tracking solution and require -185 DBW.
This dual conversion receiver can first reduce the 1575.42 MHz GPS signal to the first 37.38 MHz IF, and then convert to the second 3.78 MHz IF. The second IF is sampled using an integrated 2 or 3-bit ADC (1 bit Sing, 1 or 2-bit optional MAG), and the digitized signal is output to the baseband processor. The integrated frequency synthesizer helps to flexibly assign frequency allocation, which can be designed for 2 MHz to 26 MHz reference frequencies.Since the integrated reference vibrator is used, it can be operated in TCXO or crystal mode.
The receiver uses 2.7 V to 3.0 V power supply, and the current consumption is only 30 mA in the activation state, so energy collection sources can be used. The device uses a 28-pin QFN package that operates within the -40 ° C to + 85 ° C in the temperature range of -40 ° C to + 85 ° C under the 3 V voltage and such small volume, high integration receiver.
in conclusion
Using the latest GPS and power management ICs, modules, and antenna design, we can develop ultra-small devices that use the environment to self-powered, and this opportunity will be more and more. The solar cell is charged for lithium ion batteries and connected by a dedicated power manager to allow GPS receivers to use to more fields, bringing a variety of exciting new applications.
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