Patent ID: 7023233

Claim:
A test apparatus for testing switching speed of a circuit, which comprises a pre-stage logic element outputting a first or second level voltage and a post-stage logic element to which the output signal of the pre-stage logic element is input, comprising: a threshold voltage setting unit for setting a threshold voltage of a post-stage field effect transistor (FET) to be different from that in a normal operation by setting a substrate voltage of the post-stage FET to have a value different from that in the normal operation of the circuit; a delay time measuring unit for measuring a delay time of the circuit to which the threshold voltage different from that in the normal operation is set; and an error detecting unit for detecting an error in switching speed of the circuit based on the delay time, wherein the post-stage logic element comprises the post-stage FET, a gate terminal of which the output signal is input to, for outputting a different level of voltage according to the case that the output signal voltage is higher or lower than a predetermined threshold voltage.