This is an examination of FPGA internal differential termination resister of XILINX Spartan-6 and Virtex-5.
For reproducibility, high frequency signal is not used.
XILINX FPGA offers on-chip terminators by the name of "DIFF_TERM".
(Taken from XILINX user guide: UG381:Spartan-6 FPGA SelectIO resource user guide )
*Some pictures are copied from manufucturer's web-page.
|Item Used||Model number||Picture||Manuf.||Note|
|Spartan-6 FPGA SP601
|Virtex-5 FPGA board||XCM-203-LX30||HuMANDATA||with ZKB-016|
|Clock signal generator||CG635||Stanford Research Systems, Inc.|
|Oscilloscope||204Xi||-||Lecroy||Bandwidth limited at 200MHz|
- Waveform picture: Signal name from top: P-signal, N-signal, P minus N calclated.
- The time axis is not unified. Please see amplitude.
In case "Signal generator to Spartan-6", a DIFF_TERM did not work.
|Source Signal||FPGA||DIFF_TERM effect|
|DIFF_TERM does not work?|
Some HuMANDATA's XCM series FPGA boards did not use DIFF_TERM. They have footpatterns for on-board terminations (Not for all pins)