In the design of mobile devices, the battery operation time is an important factor. Many mobile devices add more functionality, these new features will quickly shorten the running time. The engineer must take advantage of the complex power management solutions in order to enable the battery to get the longest run time.
Engineers need to use the battery consumption analysis to assess the battery run time, this analysis needs to separate and integrated in both cases among the system down description of equipment, firmware / software and its sub-circuit. Analysis techniques including a description of the battery current consumption, as well as how to by a variety of operating modes and the use of profile. With this analysis, engineers can make power management design tradeoffs to maximize battery life.
Most of the power management system through on the sub-millisecond time scale is not in active use of the subsystem into sleep mode to save battery power. As a result, with the rapid changes in current equipment on / off events occurred in less than 1s. For example, the GSM mobile phone transmission can have the pulse of 560μs, 2A, and then when in standby mode, the current level in the sleep cycle may fall to the mA level.
Verify that the battery time-tested
Battery run-time method is to use the voltage drop test, using a fully charged battery to be verified, in the work mode of the device under test (DUT) power supply, no electricity until the battery. This test may be relatively time-consuming because it requires the whole process run is completed to determine the voltage is switched off point to determine the working hours. Similarly, the results depend on the initial state of the battery, but the latter may vary.
Another method is the implementation of current consumption measurement, it can provide higher working time measurement credibility. DUT is placed in the running for a short time in the work mode to be assessed, and measure the current consumption in this particular mode of operation. Then, the nominal battery capacity divided by the measured current consumption to calculate the working hours. Using this method, the designer need not wait for the battery to fully discharge can determine the running time.
Measurements take into account factors
The battery consumption of the power used in the analysis must be independent of the battery to describe the DUT. The power supply must have a rapid response to minimize the transient voltage drop caused by the DUT switching mode or transmit pulse rapid rotary current pulse.
Under these conditions, many common power supply may be a transient drop of up to 1V, so should be used can tolerate these conditions without a dedicated power supply voltage drop (sometimes referred to as battery simulation power).
Two measurement problems: the current waveform from the battery flows to mobile devices rapidly changing the scope and speed. First, the dynamic range of the current over a 1000:1 or even 1000, 000:1. Full power activities current in the order of magnitude of 1 ~ 3A, low sleep mode levels of current in the tens of microampere order of magnitude, so the choice of the scope of the test current to current converter has a problem. Here you can use the current perception of the resistor or shunt, but the choice of the appropriate size of the shunt may be quite difficult. If the size of the shunt is suitable for measuring the minimum current, then in the high-current events will be a large voltage drop across the shunt, which give the circuit to bring the burden of unsustainable voltage. If the size of the shunt is suitable for the measurement of large currents, when microamp current flows out of date, it is very likely not a large enough voltage available for measurement. With several shunts for different current size measurements, engineers can solve the problem of signal level, but this time switching shunt means interrupting the measurement.
Measurement speed digitizer for measuring current shunt voltage and mobile devices bias voltage should be 50kHz or higher sampling rate, in order to capture the sub-millisecond pulse, which is the complex power management program features .
Simplify the analysis
Such as 3G communication systems using complex modulation formats, which is characterized by the transmission of high data rates required for high-level amplitude modulation. Judging from the time domain, the current consumption waveform generated is complex and random.
And different operations run in a long time, the use of three data channels for transmission of a cdma2000 mobile phone RF power amplifier current consumption - time graph becomes complex and unpredictable. For battery run-time test, the situation is very common and difficult to observe the effect of changing the design of current consumption.
By looking at the statistics are taken from the current size distribution, the designer can quickly see the equipment the frequency of each current state. For the different design options, and compare these CCDF graphics, can be seen when the devices consume more energy (ie, increase in the proportion of their time in the high-current state), or when to consume less energy (that is, The said increase in the proportion of their time in the small current state). Therefore, engineers can evaluate when designing better (less energy) or to find a design flaw (unexpected need for more energy).
Several products produced by the test equipment vendors can handle different parts of the target test system. Power can be provided by the supplier to provide a stable in the extraction of fast current pulse, similar to the output of the battery.
The entry-level solution is the Agilent mobile communications DC source 66300 series. This series is specially customized for mobile devices, power supply and at the same time measure the current consumption. It integrates the battery simulation of power and similar high-speed digital oscilloscope measurement system can provide accurate current measurement device activity, standby and off mode.
This DC source and supporting turnkey software allows users without any programming, similar to the view of the oscilloscope, and data loggers view and the CCDF chart to see the current waveform. If higher accuracy and sampling rate, you can also choose other solutions provided by the company.
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