US 4,510,572 A · Signature analysis system for testing digital circuits

Abstract

A signature analyzer for testing digital circuits. The analyzer includes a memory which is initially programmed with a set of signatures characterizing the digital signals on the nodes of a correctly operating circuit. The nodes of a test circuit are then sequentially applied to a signature generator formed by a multi-stage shift register having the outputs of selected stages fed back to a gate to which the digital signal is applied. The signature generated by the shift register is compared to each of the signatures stored in memory until a signature match is found, thus indicating that the digital circuit, at least as far as the test node is concerned, is operating correctly. The signature generated by the shift register consists of twenty-four bits to provide a probability of error which is comparable to the probability of error in comparing a sixteen-bit signature with the signature from a specifically identified node. At the conclusion of a gate period, sixteen bits of the signature are displayed as four hexedecimal digits. In order to minimize the probability of error, the analyzer also counts the number of transitions of the digital signal during the gate period and compares the count to transition counts stored in memory for the digital signals on the nodes of a correctly operating circuit. A comparison is then made of the transition count at the test node with each of the transition counts stored in memory. The analyzer thus ensures a transition count match as well as a signature match.

Claims17

Dependent claims

A system for testing a digital circuit, comprising:

signature generation means receiving a digital signal from a node of said circuit for generating a signature word from said digital signal by combining each of a selected plurality of bits of said digital signature with preselected other ones of the selected plurality of bits of said digital signal;
control means for allowing said signature generation means to respond to said digital signal during a gate period which is synchronized to the operation of said digital circuit so that, at the conclusion of said gate period, said signature generation means provides a signature which characterizes said digital signal during said gate period;
signature memory means for storing respective signatures from a plurality of nodes of said digital circuit indicative of the digital signals on the nodes of said digital circuit when it is operating correctly during said gate period;
and
signature comparator means comparing the signature from said signature generation means with the signatures stored in said memory means until either a positive comparison is found or no positive comparison has been found after all of the signatures stored in said memory means have been compared, said signature comparator means generating a signature found indication in response to said positive comparison in response to all of said signatures being compared without a positive comparison.

2 more elements

An apparatus for testing a digital electronic circuit, comprising:

input means for receiving an digital signal from a selected location in said digital electronic circuit;
clock means for delivering a series of clock pulses, each pulse being coincident with a bit of said digital signal;
signature generation means connected to said input means and said clock means for generating a signature word from said digital signal by combining of a selected plurality of bits in said digital signal with preselected other ones of said selected plurality of bits of said digital signal;
trigger means connected to said digital electronic circuit and connected to said signature generation means for initiating the generation of a signature word in response to a predetermined trigger signal from digital electronic circuit at the start of a gate period;
stop means connected to said signature generation means for terminating the generation of a signature word at the end of said gate period;
memory means for recording a set of signature words corresponding to the digital signals at a set of selected locations of said digital electronic circuit when said digital electronic circuit is operating correctly during said gate period;
and
comparator means for comparing the signature word generated by said signature generation means with the signature words recorded in said memory means and for providing an indication of the results of said comparisons.

5 more elements

Dependencies are inferred from the claim text.

Signature analysis system for testing digital circuits

Life of this patent

Signature analysis system for testing digital circuits

Life of this patent

Abstract

Claims17