AN 555: True Differential Signaling Termination and Biasing for Agilex™ 7 M-Series, Agilex™ 5, and Agilex™ 3 FPGAs

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ID 776775
Date 4/23/2025
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Document Table of Contents
Document Table of Contents x
1. True Differential Signaling Termination and Biasing for Agilex™ 7 M-Series, Agilex™ 5, and Agilex™ 3 FPGAs
1. True Differential Signaling Termination and Biasing for Agilex™ 7 M-Series, Agilex™ 5, and Agilex™ 3 FPGAs x
1.1. AC Coupling and DC Coupling 1.2. TDS I/O On-Chip Termination 1.3. TDS I/O External Termination 1.4. Termination and Biasing Schemes for TDS Transmitters and Receivers 1.5. Simulation: Arria® 10 FPGA as LVDS Transmitter and Agilex™ 7 M-Series FPGA as TDS Receiver 1.6. Simulation: Cyclone® V FPGA as LVDS Transmitter and M-Series FPGA as TDS Receiver 1.7. Simulation: Agilex™ 7 M-Series FPGA as TDS Transmitter and Arria® 10 as LVDS Receiver 1.8. Summary 1.9. Document Revision History for AN 555: True Differential Signaling Termination and Biasing for Agilex™ 7 M-Series, Agilex™ 5, and Agilex™ 3 FPGAs
1.1. AC Coupling and DC Coupling x
1.1.1. Capacitors and Components Selection
1.4. Termination and Biasing Schemes for TDS Transmitters and Receivers x
1.4.1. Schematic Topology for Transmitter and Receiver Buffers 1.4.2. Recommended Topologies for TDS, LVDS, RSDS, Mini-LVDS, and LVPECL
1.5. Simulation: Arria® 10 FPGA as LVDS Transmitter and Agilex™ 7 M-Series FPGA as TDS Receiver x
1.5.1. LVDS Transmitter Interfaces with 1.3 V TDS Receiver 1.5.2. Reduced VOD LVDS Transmitter Interfaces with 1.3 V TDS Receiver Simulation Results 1.5.3. LVDS Transmitter Interfaces with 1.3 V TDS Receiver and Series Resistors 1.5.4. LVDS Transmitter Interfaces with 1.2 V TDS Receiver 1.5.5. LVDS Transmitter Interfaces with 1.2 V TDS Receiver and Series Resistors 1.5.6. LVDS Transmitter Interfaces with 1.1 V TDS Receiver and Series Resistors 1.5.7. LVDS Transmitter Interfaces with 1.05 V TDS Receiver and Series Resistors
1.6. Simulation: Cyclone® V FPGA as LVDS Transmitter and M-Series FPGA as TDS Receiver x
1.6.1. LVDS Transmitter Interfaces with 1.3 V TDS Receiver 1.6.2. LVDS Transmitter Interfaces with 1.3 V TDS Receiver and Single Attenuation Resistor 1.6.3. Minimum VOD LVDS Transmitter Interfaces with 1.3 V TDS Receiver
1.7. Simulation: Agilex™ 7 M-Series FPGA as TDS Transmitter and Arria® 10 as LVDS Receiver x
1.7.1. DC Coupled 1.3 V TDS Transmitter Interfaces with LVDS Receiver 1.7.2. AC Coupled 1.3 V TDS Transmitter Interfaces with LVDS Receiver
1. True Differential Signaling Termination and Biasing for Agilex™ 7 M-Series, Agilex™ 5, and Agilex™ 3 FPGAs

1.5.2. Reduced VOD LVDS Transmitter Interfaces with 1.3 V TDS Receiver

Figure 6. Simulation Topology (1.3 V TDS Receiver) With Reduced Transmitter VOD
Note: The DC bias circuitry uses two 50-Ω resistors to VICM. This is considered a high current biasing circuit which requires the RD OCT resistor to be disabled.

Simulation Results

Figure 7. Reduced VOD LVDS Transmitter Interfaces with 1.3 V TDS Receiver at 600 Mbps
Note:
  1. The waveform shows the VICM is within the acceptable range of the 1.3 V TDS receiver, which is between 500 mV and 1.2 V when not using RD OCT.
  2. The waveform shows a maximum input voltage of less than 1.2 V when considering the overshoot, which meets the maximum input voltage limit for this case, 1.427 V.
  3. The waveform shows a VID of less than 400 mV when considering the overshoot, which meets the maximum VID of the 1.3 V TDS receiver (454 mV). The minimum VID is 165 mV, which meets the 1.3 V TDS receiver's minimum VID requirement of 100 mV.
  4. This case demonstrates the use of a lower programmable VOD setting at the LVDS transmitter to meet the 1.3 V TDS receiver specifications. The medium-low setting is used, providing a good balance between sufficient eye opening to meet the minimum VID requirement while not exceeding the maximum VID requirement.
Figure 8. Reduced VOD LVDS Transmitter Interfaces with 1.3 V TDS Receiver at 1600 Mbps
Note:

This case again demonstrates the use of a lower programmable VOD setting at the LVDS transmitter, which can meet the 1.3 V TDS receiver specifications even up to the maximum supported data rate of 1600 Mbps.

Level Two Title