Length Mismatch

Description

Length Mismatch evaluates the difference in overall trace length between the two either two nets or the trace path between two pins in separate nets

Passing Criteria: This check passes when the absolute length difference between the two sides of the differential pair falls below a specified tolerance.

Reporting Units: Length in CENTIMETERS (cm)

Examples

Passing Message:

Failing Message:

Physics Justification

Length matching in differential pair traces is crucial for ensuring that the signals arrive at the receiver simultaneously, thus maintaining their phase alignment. In particular:

  • Noise Cancellation

    Differential pairs rely on signals being exact opposites. If they’re misaligned, they cannot cancel external noise effectively, which reduces signal integrity.

  • Avoiding Mode Conversion

    Length mismatches can convert the differential signal into common-mode noise, leading to interference and degraded performance.

  • Signal Timing

    In high-speed circuits, even small timing differences caused by mismatched lengths can introduce errors in data transmission.

Helpful Definitions

  • Phase Alignment

    This refers to two signals in a pair (like a differential pair) staying in sync and reaching their destination at the same time. Misalignment can distort the signal and cause errors.

  • Mode Conversion

    This occurs when differential signals (opposites) lose their balance because of mismatched traces, causing part of the signal to change into common-mode noise, which is unwanted.

  • Common-Mode Noise

    This is noise shared by both signals in a pair, caused by imbalances or interference, disrupting the signal the circuit is trying to read.

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