SNAA377 December   2025 LMK05318 , LMK05318B , LMK5B12204 , LMK5B12212 , LMK5B33216 , LMK5B33414 , LMK5C22212A , LMK5C23208A , LMK5C33216 , LMK5C33216A , LMK5C33414A

 

  1.   1
  2.   Trademarks
  3.   Abstract
  4. 1Introduction
  5. 2General Termination Guidelines
    1. 2.1 Identify the Driver and Receiver Requirements
    2. 2.2 Determine the Coupling Type
      1. 2.2.1 DC-Coupled Signal
      2. 2.2.2 AC-Coupled Signal
  6. 3Differential
    1. 3.1 Setting the Common-Mode Voltage (Thevenin Termination)
    2. 3.2 LVPECL
      1. 3.2.1 DC-Coupled LVPECL
      2. 3.2.2 AC-Coupled LVPECL
    3. 3.3 LVDS
      1. 3.3.1 DC-Coupled LVDS
      2. 3.3.2 AC-Coupled LVDS
    4. 3.4 HSDS
      1. 3.4.1 DC-Coupled HSDS
      2. 3.4.2 AC-Coupled HSDS
    5. 3.5 HCSL
      1. 3.5.1 DC-Coupled HCSL
      2. 3.5.2 AC-Coupled HCSL
    6. 3.6 LP-HCSL
      1. 3.6.1 DC-Coupled LP-HCSL
      2. 3.6.2 AC-Coupled LP-HCSL
  7. 4Single-Ended
    1. 4.1 LVCMOS
      1. 4.1.1 DC-Coupled LVCMOS (Series Termination)
      2. 4.1.2 AC-Coupled LVCMOS (Series Termination)
    2. 4.2 Differential P or N
      1. 4.2.1 DC-Coupled Differential P or N
  8. 5Summary
  9. 6References

2.2.1 DC-Coupled Signal

Outputs are typically DC-coupled in the following cases:

  • The receiver data sheet specifies a DC-coupled input signal.
  • The common-mode voltage and voltage swing of the driver match the receiver input specifications.
    • No need for AC-coupling capacitors.
  • The outputs are low frequency, such as 1PPS.
    • Signal distortion and/or attenuaton can occur with low frequency signal that pass through an AC-coupling capacitor. The degraded signal can violate the receiver input specification.
  • The outputs are SYSREF operating in pulser (one-shot) mode.
    • Signal distortion and/or attenuaton can occur with a pulsed signal that passes through an AC-coupling capacitor. The degraded signal can violate the receiver input specification.
  • Fast rise times are of high importance.
    • Rise times are reduced when AC-coupling capacitors are introuced in the signal path.

DC-coupled outputs can be terminated on either the driver or receiver side. High speed differential signals (such as LVDS) are load terminated which means termination is typically near the receiver. However, termination placement generally does not matter as long as the impedance of the signal matches the transmission line impedance.

Example of DC-Coupled Termination on the Driver SideFigure 2-1 Example of DC-Coupled Termination on the Driver Side
Example of DC-Coupled Termination on the Receiver SideFigure 2-2 Example of DC-Coupled Termination on the Receiver Side