Timing generator, and timing generating method

A test apparatus testing a device under test, comprising:

• a pattern generating unit for supplying a test pattern to the device under test according to a given timing signal;
• a signal detector for detecting a signal value of an output signal output from the device under test according to the test pattern at the timing of a given strobe signal;
• a timing generator for generating the timing signal and the strobe signal and supplying these signals to said pattern generating unit and said signal detector;
• and
• a decider for deciding the good or bad of the device under test based on the signal value detected from said signal detector, wherein
• said timing generator comprises:
• a first voltage-controlled oscillating unit for outputting an oscillation signal with frequency according to a given control voltage as the timing signal;
• a second voltage-controlled oscillating unit for outputting an oscillation signal with frequency according to a given control voltage as the strobe signal;
• and
• a timing controlling unit for superimposing a superimposed voltage according to the phase difference between a strobe signal and the timing signal, on the control voltage in order to supply the voltage to the first voltage-controlled oscillating unit and the second voltage-controlled oscillating unit,
• the timing controlling unit comprises:
• an initializing unit for measuring a timing shift gain indicative of a ratio of a timing shift amount of the oscillation signal, which is output from the first voltage-controlled oscillating unit and the second voltage-controlled oscillating unit, to a change of the superimposed voltage;
• and
• a voltage generating unit for generating the superimposed voltage based on a timing shift amount according to phase difference between the strobe signal and the timing signal and the timing shift gain, and
• the initializing unit comprises:
• a first phase adjusting means for shifting a phase of at least one of the timing signal and the strobe signal with respect to a phase of the other and harmonizing the phase of the timing signal with the phase of the strobe signal;
• a second phase adjusting means for sequentially changing the superimposed voltage supplied by the voltage generating unit to the voltage-controlled oscillating unit and detecting an amount of change of the superimposed voltage when the phase of the first periodic signal and the phase of the second periodic signal are identical with each other once more, on condition that an amount of phase shift by the first phase adjusting means is held;
• and
• a gain computing unit for computing the timing shift gain based on an amount of change of phase of the second periodic signal to the first periodic signal caused by changing the change amount of the superimposed voltage detected from the second phase adjusting means and the superimposed voltage.

A timing generating method of generating a second periodic signal having a predetermined phase difference to a first periodic signal, comprising:

• a voltage-controlled oscillating step of outputting an oscillation signal with frequency according to a given control voltage as the second periodic signal;
• and
• a timing controlling step of superimposing a superimposed voltage according to the phase difference of the second periodic signal to the first periodic signal on the control voltage in order to supply the voltage to said voltage-controlled oscillating step, wherein
• said timing controlling step comprises:
• an initializing step of measuring a timing shift gain indicative of a ratio of a timing shift amount of the oscillation signal output from said voltage-controlled oscillating step to a change of the superimposed voltage;
• and
• a voltage generating step of generating the superimposed voltage based on a timing shift amount according to the predetermined phase difference of the second periodic signal and the timing shift gain, and
• the initializing step comprises:
• a first phase adjusting step of shifting a phase of at least one of the first periodic signal and the second periodic signal with respect to a phase of the other and harmonizing the phase of the first periodic signal with the phase of the second periodic signal;
• a second phase adjusting step of sequentially changing the superimposed voltage supplied by the voltage generating step to said voltage-controlled oscillating step and detecting an amount of change of the superimposed voltage when the phase of the first periodic signal and the phase of the second periodic signal are identical with each other once more, on condition that an amount of phase shift in the first phase adjusting step is held;
• and
• a gain computing step of computing the timing shift gain based on an amount of change of phase of the second periodic signal to the first periodic signal caused by changing the change amount of the superimposed voltage detected in the second phase adjusting step and the superimposed voltage.