Have you ever made these mistakes in in circuit design?----The low-power design

Sunday, February 5, 2017

P1: Our system is the 220V power supply,so i do not need to care about power consumption.

Analysis : Saving power is not the only benefit of using Low-power design.More benefits are to reduce the costs of the power module and cooling system.Due to the current reduction, it also reduces the interference of electromagnetic radiation and thermal noise. As the temperature of the device decreases, the life of the device is relatively extended ( Each 10℃ increase in temperature, half the lifetime was shortened).

P2：How to deal with these unused I/O port of the CPU and FPGA?Just ignore it in a short time.

Analysis: if you ignore the I / O port, it is possible that it will produce repeated oscillation of the input signal by a little bit of interference from the outside world.The power consumption of MOS basically depends on the number of flip-flop gate. If you pull it up, each pin will also have the current of microamps, so the best way is to set it to be the output (of course, the outside can not access other drive signals).

P3: I should make use of the gate of FPGA.

Analysis: The FGPA power consumption is proportional to the number of flip-flops used and its flip.As a result, it is possible that there is a tenfold variation in their power consumption,even with the same type of FPGA in a different circuit at different times.Minimizing the number of high-speed flip-flops is the fundamental method to reduce the power consumption.

P4： I do not need to consider the power consumption of these small and low-power chips.

Analysis: The power consumption of those chips with relatively simple internal structure is difficult to measure.it is mainly determined by the current on the pin.For example, an ABT16244, no load, maybe the power consumption is less than 1 mA, but its foot can drive 60 mA load.In other words,the full load power consumption can up to 60 * 16 = 960mA .

P5: Most of the signals have overshoot .it is necessary to accurately match them.

Analysis: In addition to a few specific signals (such as 100BASE-T, CML), most of the signals have overshoot,but it is not necessary to match them if the signals are small.For example, the output impedance of TTL less than 50 ohms, even 20 ohms. if we use such a large matching resistor, the current will be very large,as same as power consumption.At the same time,the other signal amplitude will be too small to be used. Therefore, it is better to match them within an acceptable limit, such as TTL, LVDS, 422 and other signals.

P6: We should reduce the power consumption by improving hardware,rather than software.

Analysis:The software nearly controls all of the chips and signals on the bus. if the software can reduce the number of external memory access (make full use of register variables and internal CACHE, etc.), timely response to the interruptions and other specific measures will greatly contribute to reducing the power consumption.

Author ：Darcy Beaufort