GTS Transceiver PHY User Guide: Agilex™ 5 FPGAs and SoCs

ID 817660
Date 4/07/2025
Public
Document Table of Contents

2.3.2.1. Receiver Buffer and Equalizer

The receiver analog front end is shown in the following figure.
Figure 19. Simplified Receiver Analog Front End
The various capacitors and resistors for the receiver analog front end are described below:
  1. You can implement on board AC coupling capacitors, Con-board, based on applicable standards.
  2. Con-chip, on-chip AC coupling capacitor is 1pF. It is always on and is only bypassed in SDI mode. There is an equivalent 4 MΩ resistor after the on-chip 1 pF AC coupling capacitor, which creates a cut-off frequency:

    fc =1 / (2 * pi * RC) = ~40 kHz

  3. RDIFF-DC, DC differential receive impedance is programmable to 85Ω or 100Ω.
  4. When you implement on-board AC coupling capacitors you must set the RX termination mode to ground termination. When it is DC coupled and no on-board AC coupling capacitors are implemented, set the RX termination mode to differential. Receiver input DC common mode voltage (non SDI mode) at the RX FPGA pins must be:
    1. Smaller than 700mV, if squelch detect is not used.
    2. Must be between 200mV to 300mV, if squelch detect is used.
Note: Refer to Configurable Quartus® Prime Settings or Analog Parameter Options for details about how to set the RX termination mode.
The receiver buffer receives serial data from input pins and feeds it to the CDR block and deserializer. To optimize the bit error rate (BER) for optimum performance, receiver equalization supports adaptive and manual tuning.