METHOD FOR MEASURING INPUT THRESHOLD VOLTAGE OF LOGIC INTEGRATED CIRCUIT AND METHOD FOR DECIDING WHETHER OR NOT CHARACTERISTIC OF INPUT THRESHOLD VOLTAGE IS CONFORMING

摘要

PURPOSE:To enable measurement of the input threshold voltage of a circuit so as to make a judgement as to whether characteristics of the FFs are conforming or nonconforming by gradually lowering or raising the voltage of a control signal which decides whether FFs are in their enable or disable state. CONSTITUTION:FFs 2-4 are switched to their disable state at the H level of control voltages applied to the FFs 2-4 and to their enable state at the L level. A control signal is gradually lowered from the H level and at the input of the control signal the FFs 2-4 are changed to their enable state when the signal is lowered below the threshold voltage of the gate 5 of an input portion, and the FFs start to operate simultaneously in response to a scan-in input signal. Therefore source current is suddenly increased at that point of time. The voltage of the control signal at that time is an input threshold voltage. By measuring the voltage the input threshold voltage of each of the input terminals of a logic integrated circuit 1 can be simply detected. There is no influence of noise particularly when the FFs are changed from their disable to enable state.