We often find some rules or principles that we take for granted will be some errors. Electronic engineers in pcb design will have such examples. The following eight errors are a summary of an engineer.
Error 1: requirement of PCB board design is not high,so use a little fine line, and do the routing automatically.
Comments: The automatic routing is necessary to occupy a larger area of PCB, while it generate more times vias than manual routing. In large quantities of products,factors ,which PCB factory consider for reducing price ,in addition to the commercial factor,are line width and the number of through holes,which are affecting the yield of PCB and consumption of PCB drill.Saving the cost of the supplier also finds a reason to cut prices.
Error 2: These bus signals are used resistance to pull, and feel more ease
Comments: The reasons for the drop-down signal and the drop-up signal are many, but not all have to pull.Pulling a mere input signal need the current of tens of micro amps or less.But pulling a driven signal need milliamps.If pull all the resistance, a few watts of power consumption are all in the resistance.
Error 3: how to handle I/O port that CPU and FPGA can not use? Let it empty now, maybe better.
Comments:if unused I / O port is vacant, subject to outside a litter interference,it may become the input signal of repetitive oscillation , while the power consumption of the MOS device depends on the number of times of turns. If you pull on it, every pin will have microampere currents, so the best way is to set to output ,and of course, there is no other driven signal outside.
Error 4: The FPGA left too much gate to use up, you can enjoy the play.
Comments: The power consumption of FGPA is proportional to the number of triggers used and the number of turns,so the power consumption of the same type of FPGA may vary by 100 times in different circuits at different times . Minimizing the number of high-speed triggers is the basic method to reduce FPGA power consumption.
Error 5: the power consumption of these small chip is very low,so do not consider them.
Comments: It is difficult for less complex internal chip to determine power consumption.It is mainly determined by the current on pin.A ABT16244, if there is no load ,its power consumption is less than about 1 mA,but its indicator is that each pin can drive 60 mA of load (such as matching tens of ohms),namely full load power consumption is up to 60 * 16 = 960mA, of course, it is just the supply current, and the heat fell on the load .
Error 6: memory has so much control signal. I only need OE and WE signal on this board ,so chip select can connect the ground,so that we read out data faster.
Comments: the power consumption of most memory with effective chip select is more than 100 times than that with ineffective chip select.So it should be possible to use CS control chip,and in the case of meeting other requirements, we should try to reduce the width of the chip select pulse.
Error 7: why do these signals have overshoot? As long as the match is well, it can be eliminated
Comments: In addition to a small number of specific external signals (such as 100BASE-T, CML),there all have overshoot.If it is not great, it is not necessary to match. Even if you want to match,it is not necessary to match the best. Like TTL ,its output impedance is less than 50 ohms, or 20 ohms.If so big matched resistance is also used,the current is very large,and the power consumption is unacceptable.While the amplitude of the signal will be too small to be used.Besides output impedance when general signal output the high level is not the same when general signal output the low level.There is no way to do an exact match. So for the match of the TTL, LVDS, 422 ,juts do as the overshoot can be acceptable.
Error 8: reducing power consumption is the matter of hardware personnel , and the software does not matter
Comments: Hardware just take a stage, software is singing . Software amost controls visit of every chip and turns of every signal.If the software can reduce the external memory access times (multi-use register variables, multi-use internal CACHE, etc.),it will contribute greatly to reduce power consumption.