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

3.2.2 AC-Coupled LVPECL

Apply AC-coupling capacitors to the LVPECL output when interfacing with non-LVPECL receivers and/or to reconfigure the VCM.

Example Termination

For a traditional LVPECL driver, a DC return path is required. Place emitter resistors (140 to 220Ω, typically 150Ω) to ground on the driver side to maintain the current path. Then, add AC-coupling capacitors to separate the DC bias from the driver. Use a Thevenin termination to provide a new bias voltage that is less than VCC – 1.3V. The bias voltage activates the gates of the emitter-follower pair from the LVPECL input stage. See Section 3.1.2 Input Stage for Devices Using LVPECL Drivers inInterfacing Between LVPECL, VML, CML and LVDS Levels.

AC-Coupled LVPECL to LVPECL

AC-Coupled LVPECL to LVPECL Using a Thevenin Termination Figure 3-7 AC-Coupled LVPECL to LVPECL Using a Thevenin Termination

AC-Coupled AC-LVPECL to LVPECL

For AC-LVPECL type outputs (as seen in LMK05318B), termination before the AC-coupling capacitors is not required because the driver is internally biased and terminated. The capacitors can be placed on the receiver or driver side. Do not DC-couple the signal unless the output VCM meets the receiver specification.

AC-Coupled AC-LVPECL to LVPECL Using a Thevenin Termination Figure 3-8 AC-Coupled AC-LVPECL to LVPECL Using a Thevenin Termination