Skew adjusting method, skew adjusting apparatus, and test apparatus

A skew adjusting method for adjusting a skew between a positive-side differential signal and a negative-side differential signal in differential signals inputted from an outside device via outside transmission lines;

• comprising:
• a step of positive-side transmission for propagating said positive-side differential signal inputted to an input end by a positive-side transmission line;
• a step of negative-side transmission for propagating said negative-side differential signal inputted to an input end by a negative-side transmission line;
• a step of taking in said positive-side differential signal and said negative-side differential signal by a plurality of differential comparators connected with said positive-side and negative-side transmission lines so that a wiring length from the input end of said positive-side transmission line to one of the plurality of differential comparators and a wiring length from the input end of said negative-side transmission line to the one of the plurality of differential comparators is different from each other;
• and
• a step of selection for selecting a signal outputted by said differential comparator by which a skew between a positive-side path from an output terminal of said positive-side differential signal in said outside device to said differential comparator and a negative-side path from an output terminal of said negative-side differential signal in said outside device to said differential comparator is minimized,
• wherein the step of selection includes:
• a step of inputting an adjusting differential signal substantially having no skew between a positive-side differential signal and a negative-side differential signal of the adjusting differential signal to end parts of the outside transmission lines, wherein the outside device is to be connected to the end parts;
• and
• a step of selecting one of said differential comparators where said skew becomes least based on said adjusting differential signal obtained by each of said plurality of differential comparators.

A test apparatus for testing a semiconductor device-under test, comprising:

• a pattern generator for generating a test pattern of said semiconductor device-under test;
• a waveform shaper for generating a test signal to be supplied to said semiconductor device-under test by forming said test pattern;
• a signal output section for supplying said test signal to said semiconductor device-under test;
• a skew adjusting section for inputting differential signals outputted out of said semiconductor device-under test via transmission lines to adjust a skew between a positive-side differential signal and a negative-side differential signal in said differential signal;
• and
• a judging section for judging whether said semiconductor device-under test is defect-free based on said differential signal inputted by said skew adjusting section, wherein the skew adjusting section includes:
• a positive-side transmission line for propagating said positive-side differential signal inputted to the input end;
• a negative-side transmission line for propagating said negative-side differential signal inputted to the input end;
• a plurality of differential comparators that is connected to said positive-side and negative-side transmission lines so that a wiring length from the input end of said positive-side transmission line to one of the plurality of differential comparators and a wiring length from the input end of said negative-side transmission line to the one of the plurality of the differential comparators are different from each other and that takes in said positive-side differential signal and said negative-side differential signal;
• and
• a selecting section for selecting a signal taken in by said differential comparator where the skew between the negative-side path from an output terminal of said positive-side differential signal in said semiconductor device-under test to said differential comparator and the negative-side path from the output end of said negative-side differential signal in said outside device to said differential comparator is minimized,
• wherein the positive-side transmission line comprises the input end, which is to be connected to the outside device and receives differential signals from the outside device, and a non-input end which is another end of the positive-side transmission line and receives no differential signals from the outside device, and the negative-side transmission line comprises the input end which is to be connected to the outside device and receives differential signals from the outside device and a non-input end which is another end of the negative-side transmission line and receives no differential signals from the outside device,
• the skew adjusting apparatus further comprising an adjusting signal output section for supplying an adjusting differential signal to the non-input end of said positive-side transmission line and to the non-input end of said negative-side transmission line,
• wherein the selecting section selects a combination of said positive-side junction and said negative-side junction that minimize said skew based on said adjusting differential signal reflected from end parts of the outside transmission lines, wherein the outside device is to be connected to the end parts.

A skew adjusting apparatus, comprising:

• two delay lines to which differential signals outputted out of a semiconductor device-under test are applied;
• a plurality of junctions in ascending order, provided per predetermined distance from an apply point of said differential signal on one of said two delay lines, for taking out differential signals in which delay time of said differential signals increases in ascending order from said apply point;
• a plurality of junctions in descending order, provided per predetermined distance from a non-apply point of said differential signal on the other delay line, for taking out differential signals in which delay time of said differential signals decreases in descending order from said apply point;
• a plurality of differential comparators for taking in the differential signal from each one of the plurality of junctions in ascending order and the plurality of junctions in descending order correlated from each other;
• and
• a selecting section for selecting a judgment result out of judgment results outputted out of said plurality of differential comparators,
• wherein the respective delay lines comprises an input end, which is to be connected to the semiconductor device under test and receives differential signals from the semiconductor device under test, and a non-input end which is another end of the respective delay lines and receives no differential signals from the semiconductor device-under-test,
• the skew adjusting apparatus further comprising an adjusting signal output section for supplying an adjusting differential signal to the non-input ends of the delay lines,
• wherein the selecting section selects a pair of junctions on the delay lines that minimize said skew based on said adjusting differential signal reflected from end parts of the delay lines, wherein the semiconductor device under test is to be connected to the end parts.