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I am looking for recommendation of a converter/cable to convert a digital pulse to LVDS. Attachment is the schematic of the whole design. enter image description here Basically, my task is to measure the photon arrival time, which means to read the time different between a reference signal (REF) and a STOP signal. The REF signal is 3.3 V, 10ns pulse generated by Waveform Generator. The STOP signal is 3.3V pulse, 10 ns width, around 10MHz to 1GHz generated by a Single Photon Detector. I am using a time-to-digital convert chip (GPX2 TDC) which accepts LVDS inputs, therefore, I need to convert my REF and STOP signals to LVDS signals to do the time measurement. Just to clarify my design, the time measured is output from this TDC chip is sent by LVDS interface to Spartan 6 FPGA. I need to write VHDL code to read this time and output it to a PC. Thank you.

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  • \$\begingroup\$ Which "my signal" is analog (a schematic might help explain your problem better)? LVDS is a digital format. If you want to convert an analog signal to digital you need an ADC or a comparator (which loses a lot of information about the signal). \$\endgroup\$
    – The Photon
    Dec 6, 2017 at 16:40
  • \$\begingroup\$ Thank you. My signal is analog pulse, 3.3V. Can I just use a LVDS driver? \$\endgroup\$
    – Lac
    Dec 6, 2017 at 16:42
  • \$\begingroup\$ If the signal is always either 0 V or 3.3 V, I don't understand why you call it an analog pulse and not a digital pulse. Since I don't understand your application, I can't make any recommendation about it. \$\endgroup\$
    – The Photon
    Dec 6, 2017 at 16:51
  • \$\begingroup\$ For example if you explained (by editing your question) what device is generating the pulse, what possible values it has, how long the pulse lasts, what you want the new circuit to do when the input has different voltages, etc., then it's likely we'll be able to give you a useful answer. \$\endgroup\$
    – The Photon
    Dec 6, 2017 at 17:00
  • \$\begingroup\$ @ThePhoton I have edit my question and added a diagram. Thanks a lot for your help. \$\endgroup\$
    – Lac
    Dec 6, 2017 at 17:31

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Use a high speed comparator with differential outputs, eg ADCMP561. If your TDC cannot accomodate LVPECL, then an LVPECL to LVDS converter from Onsemi should do the job. Build everything on a 4 layer board, better a 6 layer board and treat everything as an high frequency system with a frequency of the inverse of your TDC resolution (eg 20ps resolution -> 50GHz system), otherwise you are up for some (statistically) significant crosstalk between the measurement paths.

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