Target value search circuit, taget value search method, and semiconductor test device using the same

A method of searching for a target value, comprising:

• a step of storing a target value;
• a step of extracting the target value, and setting, as a tentative target value, a value obtained by subtracting a predetermined value from the extracted target value or adding the predetermined value thereto;
• a step of limiting a searching range to a certain region including the tentative target value by binary search;
• and
• a step of searching for the target value in an increasing or decreasing direction from the tentative target value which is a start point in the limited searching range by sequential search.

A semiconductor test apparatus comprising:

• a reference clock generation unit which generates a reference clock signal;
• a test pattern generation unit which outputs a test pattern signal applied to a semiconductor device in synchronization with the reference clock signal;
• a timing generation unit comprising a variable delay circuit which delays the test pattern signal by a predetermined time;
• a comparison unit which compares a response output signal output from the semiconductor device with an expected value pattern;
• and
• a search circuit comprising:
• a storage section which stores a target value;
• a delay amount measurement section which obtains a delay amount measured value of the test pattern signal;
• a tentative target value calculation section which extracts the target value from the storage section and which calculates, as a tentative target value, a value obtained by subtracting a predetermined value from the extracted target value or adding the predetermined value thereto;
• a binary search executing section which applies a delay amount set value of the variable delay circuit in such a manner as to limit a searching range to a certain region including the tentative target value by binary search;
• a sequential search executing section which applies the delay amount set value of the variable delay circuit in such a manner as to search for the target value in an increasing or decreasing direction from the tentative target value which is a start point in the limited searching range by sequential search;
• a VD setting section which sets a delay amount of the variable delay circuit;
• and
• a search control section which sends the tentative target value and the delay amount measured value to the binary search executing section and which sends the delay amount set value from the binary search executing section to the VD setting section to set the delay amount of the variable delay circuit and which sends the delay amount set value, the target value, and the delay amount measured value, obtained by limiting, to the sequential search executing section, when the searching range is limited to the certain region including the tentative target value and which sends the delay amount set value from the sequential search executing section to the VD setting section to set the delay amount of the variable delay circuit.