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Characterizing Circuit Delay as a Function of Signal Integrity

IP.com Disclosure Number: IPCOM000113564D
Original Publication Date: 1994-Sep-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 79K

IBM

Related People

Dougherty, JM: AUTHOR [+1]

Abstract

Accurately estimating a circuit delay based upon its transitioning input waveform requires that input irregularities be considered when characterizing the circuit. Slope reversal and plateauing on a transitioning input signal after it has passed through the switch threshold may significantly increase delay through a circuit. Disclosed is a method for characterizing circuit delay as a function of signal integrity.

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Characterizing Circuit Delay as a Function of Signal Integrity

Examples of Circuit Inputs and Outputs

Accurately estimating a circuit delay based upon its
transitioning input waveform requires that input irregularities be
considered when characterizing the circuit.  Slope reversal and
plateauing on a transitioning input signal after it has passed
through the switch threshold may significantly increase delay through
a circuit.  Disclosed is a method for characterizing circuit delay as
a function of signal integrity.

Circuit delays are often characterized as a function of circuit
input transition time.  This allows the designer to simulate a
network which drives several circuits without the need for detailed
circuit models (simple capacitive loads will suffice).  This reduces
the simulation model complexity and, in turn, decreases simulation
run time.

Input transition time, however, is not the only parameter which
affects the delay through a circuit.  Slope reversal and plateauing
on a transitioning input signal may introduce a significant delay
adder.  The added delay due to these "glitches" is best illustrated
by example.  Shown in figure are three input waveforms labeled Ain,
Bin, and Cin.  These three inputs were applied to the input of an
inverting receiver circuit.  The corresponding outputs are labeled
Aout, Bout, and Cout, respectively.  (Note: the input waveforms have
been shifted by 5 volts in the Figure so as not to overlap with the
output waveforms).  All three inputs h...