Application Notes: PECL and LVDS Outputs




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Latest News | March 29, 2017

Application Notes: PECL and LVDS Outputs

Application Notes: PECL and LVDS Outputs

 

What are PECL and LVPECL?

  • - PECL stands for “Positive Emitter Coupled Logic”. PECL are differential logic outputs commonly used in high-speed clock distribution circuits. PECL requires a +5V supply.
  • - Low Voltage PECL (LVPECL) denotes PECL circuits designed for use with 3.3V or 2.5V supply, the same supply voltage as for low voltage CMOS devices.
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    Pros/Cons of PECL Output

  • Advantages:
  • - Very good jitter performance due to large voltage swing
  • - Ideal use in high-speed circuits
  • - Capable of driving long transmission lines

  • Drawbacks:
  • - Larger power consumption due to differential output and external DC biasing compared to single-ended output
  • - Incompatible with 1.8V supply
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    Recommended PECL Termination Circuit

  • Each output is terminated with a 50Ω resistor to a termination voltage of (Vdd – 2V).
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    What is LVDS Output?

  • - LVDS stands for Low Voltage Differential Signaling, centered around operating voltage of 1.2V, regardless of power supply.
  • - LVDS technology is defined by the ANSI/TIA/EIA- 644 industry standard.
  • - Dynamic Engineers (DEI) has many crystal oscillator product lines with LVDS output options at 3.3V and 2.5V supplies.
  •  

    Pros/Cons of LVDS Output

  • Advantages:
  • - LVDS stands for Low Voltage Differential Signaling, centered around operating voltage of 1.2V, regardless of power supply.
  • - LVDS technology is defined by the ANSI/TIA/EIA- 644 industry standard.
  • - Dynamic Engineers (DEI) has many crystal oscillator product lines with LVDS output options at 3.3V and 2.5V supplies.

  • Drawbacks:
  • - Reduced jitter performance compared to PECL
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    Where is LVDS used?

  • The LVDS standard was created to address applications in the data communications, telecommunications, server, peripheral and computer markets where high-speed data transfer is necessary.
  •  

    Recommended LVDS Termination Circuit

  • A single 100Ω termination resistor is needed. Some receiver ICs may include the resistor internally.
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    Single Level Comparison

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