Honored ContributorHi everyone,
I'm trying to collect traces of power consumptions for different instructions that is executed on the FPGA. I would most probably be using a digital oscilloscope(1Ghz). I read I need to connect a series resistor to the GND or power supply. How to I do this and where is the best point on the DE1 board to place my probes? Thanks.
Honored ContributorHi, to measure the current drained by the board you need to place a series (shunt) resistor on the power supply line.
The current will be the voltage across the shunt resistor divided by the resistance value itself. It must be a very low resistance with high accuracy (value: as low as possible) so that it does not affect the real current drained. You may put it on the main power supply line, but in that case you will measure the total current drained by the board. If you need to know the current that only the FPGA uses, you will need to put a shunt resistor on the FPGA core supply line (you have to identify the voltage regulator on the board), check a suitable point to interrupt the supply path and insert the resistance. Good luck!Honored Contributorthanks for the reply~
Honored Contributores to measure the current you need to do measure in series with the board, by useing a scope or a meter. I will explain the problems with each.
If you are just wanting a simple value of the current used then use an ammeter in series with the board or sub section of the board. Most digital ammeters will be fine for this. If you are wanting to measure the current then you will either need to insert a low value resistor and measure the voltage across it, or use a scope current probe. The low value resistor approach can be difficult as the measured voltages will be very small and there will be a lot of noise about. You will do better if you reduce the bandwidth on the scope to say 20MHz or less. A current probe is easy to use you just put the wire you want to test in the probe and it is displayed on the scope. Get back to me if you need more info. Uk FixerHonored ContributorIf you check the DE1 schematics thorougly, you'll notice that it has 0-ohm-jumpers for VCCINT and VCCIO. They can be replaced by low-ohm (0.1 ohm maximum) shunt resistors and allow a precise measurement.
A dynamical measurement as dicussed previously discussed could be done only at a slow (e. g. ms) time scale, cause high capacitance decoupling capacitors are connected directly to the power planes. A undistorted dynamic measurement of FPGA supply currents is basically impossible on a regular board, to my opinion. I also think, that the dynamic effects of fast currents transients (ground and supply bounce) can be better observed indirectly at I/O pins.
