AN 555: True Differential Signaling Termination and Biasing for Intel Agilex® 7 M-Series and Intel Agilex® 5 FPGAs

Download PDF
ID 776775
Date 5/19/2023
Public
Document Table of Contents
Document Table of Contents x
True Differential Signaling Termination and Biasing for Intel Agilex® 7 M-Series and Intel Agilex® 5 FPGAs
True Differential Signaling Termination and Biasing for Intel Agilex® 7 M-Series and Intel Agilex® 5 FPGAs x
AC Coupling and DC Coupling TDS I/O On-Chip Termination TDS I/O External Termination Termination and Biasing Schemes for TDS Transmitters and Receivers Simulation: Intel Agilex® 7 M-Series FPGA as TDS Receiver Simulation: Intel Agilex® 7 M-Series FPGA as TDS Transmitter Summary Document Revision History for AN 555: True Differential Signaling Termination and Biasing for Intel Agilex® 7 M-Series and Intel Agilex® 5 FPGAs
AC Coupling and DC Coupling x
Capacitors and Components Selection
Termination and Biasing Schemes for TDS Transmitters and Receivers x
Schematic Topology for Transmitter and Receiver Buffers Recommended Topologies for TDS, LVDS, RSDS, Mini-LVDS, and LVPECL
Simulation: Intel Agilex® 7 M-Series FPGA as TDS Receiver x
Simulation Results
Simulation: Intel Agilex® 7 M-Series FPGA as TDS Transmitter x
Simulation Results
True Differential Signaling Termination and Biasing for Intel Agilex® 7 M-Series and Intel Agilex® 5 FPGAs

AC Coupling and DC Coupling

In AC coupling, a series capacitor blocks the DC signals from going through. In DC coupling, the series capacitor is not present and the signal passes through uninterrupted.

AC coupling allows chips with different common-mode voltages to interface with each other. However, it requires a capacitor. If you do not select a proper capacitor, AC coupling can add jitter or degrades the signal. After the series capacitor, you need a DC restore circuit to meet the common-mode voltage requirements of the receiver.

Note: Intel recommends that you use SPICE or IBIS models to verify your capacitor selection.

DC coupling works in cases where the output common-mode voltage of the transmitter is in the required range of the input common-mode voltage of the receiver.

  • Use DC coupling if you are certain that the common-mode voltage requirements of the transmitter are a subset of the common-mode voltage output of the receiver.
  • Use AC coupling if your case is borderline or the requirements are not satisfied.
Note: If you use AC coupling, you must transmit DC-balanced data. The 8b/10b encoding is commonly used for AC-coupled interfaces.

Section Content
Capacitors and Components Selection

Related Information
Level Two Title