GUIDELINES FOR LOGICAL AND LEGISLATIVE STRUCTURE TESTING DIGITAL LOGICAL ACTIVITIES

摘要

An apparatus for performing logic and leakage current tests on a logic circuit device under test (DUT) includes a local module for each terminal of the DUT. For performing logic test, each local module has a driver for supplying a logic signal input to the DUT terminal, a comparator for detecting the DUT output at the terminal, and a clamping circuit for limiting the voltage swing at the DUT terminal during the logic test. For performing a leakage current test, each local module includes a source for supplying a parametric signal to the DUT terminal. The voltage the parametric signal produces at the DUT terminal, as detected by the comparator, indicates the terminal's leakage current. The parametric signal source and the clamping circuit are connected to the DUT terminal through Schottky diodes. During a logic test the parametric signal source is isolated from the DUT terminal by reverse biasing the Schottky diodes linking the parametric signal source to the DUT terminal. Conversely, during a leakage current test, the clamping circuit is isolated from the DUT terminal by reverse biasing the Schottky diodes linking it to the DUT terminal. The Schottky diodes, when reverse biased, have very low capacitance and leakage current. Thus a DUT terminal leakage current measurement is not substantially influenced by leakage current through the clamping circuit and the edges of logic signal pulses are not substantially affected by capacitance added to the DUT terminal by the parametric signal source.