Delay time measuring device for circuit for testing semiconductor components

摘要

The device has a voltage controlled oscillator (10) whose oscillating frequency is controlled by an applied voltage. It also has a phase comparator (40) with two inputs to compare a phase difference between signals at the two inputs. One input receives an output signal of the oscillator (10) via a delay circuit (200) whose delay time is to be measured. The other input receives the oscillator output directly. The oscillator (10) and the phase comparator (40) are connected in a phase control loop. The loop feeds back an output voltage of the comparator (40) to the oscillator (10) to control its oscillation frequency. The voltage is fed back such that the phase difference between the two input signals of the comparator becomes zero. The device also has a signal adder (60) to feed an external signal into the phase control loop to vary the oscillation frequency. The external signal is a signal whose average voltage level is zero for a whole number multiple of one cycle. The device also has a counter (20) to count the oscillation frequency of the oscillator (10).