Scan-based delay tests having enhanced test vector pattern generation

Abstract

This invention teaches circuitry and methods for performing delay tests, including skewed-load, broad-side, and STUMPS-related tests. More particularly a logic circuit (10), such as an integrated circuit, includes at least one block of combinational logic (12) having a plurality of input nodes and at least one output node. The logic circuit further includes delay test circuitry (14, 16, 18) that is coupled to the plurality of input nodes and to the at least one output node. The delay test circuitry has a scan-chain register (14) having a plurality of outputs coupled to the plurality of input nodes for establishing at least first and second multi-bit test vectors at the plurality of input nodes. The delay test circuitry further includes a plurality of XOR gates that are coupled to the scan-chain register. The plurality of XOR gates have outputs for establishing logic states of bits of the second test vector at the plurality of input nodes. In the skewed-load test the XOR gates overcome the one bit shift dependency problem, while in the broad-side and STUMPS test the XOR gates, in combination with one or more sources of random logic states, are used to introduce second vectors having optimal probabilities for launching transitions.