US 5,854,804 A · Method and apparatus for synchronizing a mode locked laser with a device under test

Abstract

A method and an apparatus for synchronizing a mode locked laser with a device under test. The present invention provides a stroboscopic technique that synchronizes the free running laser pulses of a mode locked laser to a DUT enabling the optical testing of integrated circuits to be performed and waveform measurements to be acquired from a DUT at random operating frequencies. In one embodiment, a laser synchronizing apparatus is configured to be used to test a device under test . The laser synchronizing apparatus includes a mode locked laser generating repeating laser pulses having a first period. A test pattern operating in M clocks when executed on the device under test is constructed. M is an integer and each one of the M clocks has a second period. A time per test pattern is computed such that the time per test pattern provides a sufficient amount of time to execute the constructed test pattern operating in the M clocks. The time per test pattern is a common multiple of the first period and the second period such that N laser pulses are generated during the time per test pattern with N being an integer. The test pattern is looped on the device under test with the laser synchronizing apparatus synchronized with the mode locked laser and each loop of the test pattern taking the time per test pattern to execute.

Claims28

Dependent claims

A method for synchronizing a mode locked laser generating repeating laser pulses having a fixed period with a device under test (DUT), the method comprising the steps of:

constructing a test pattern operating in M clocks when executed on the DUT, M being an integer and each one of the M clocks has a second period;
computing a time per test pattern, the time per test pattern being a common multiple of the fixed period and the second period such that N laser pulses are generated during the time per test pattern, N being an integer;
and
looping the test pattern on the DUT with the mode locked laser such that the laser pulses remain in a fixed and stable phase relationship to the DUT clock.

1 more element

A laser synchronizing apparatus configured to test a device under test (DUT), comprising:

a mode locked laser generating repeating laser pulses;
a switch configured to select at least one sampling pulse from the repeating laser pulses to stroboscopically sample a waveform from the DUT;
a counter coupled to the switch and configured to count the repeating laser pulses generated by the mode locked laser;
a trigger signal configured to control clocking of the DUT;
a phase lock loop coupled to the switch, the mode locked laser, and coupled to receive the trigger signal, the phase locked loop configured to synchronize the repeating laser pulses with the trigger signal;
and
a delay generator coupled to the phase lock loop to control a phase difference between the trigger signal and the repeating laser pulses;
wherein the laser synchronizing apparatus is configured to loop a test pattern to test the DUT, each loop of the test pattern taking M clocks to execute, M being an integer, the mode locked laser generating N pulses during each loop of the test pattern, N being an integer.

5 more elements

A laser synchronizing apparatus configured to test a device under test (DUT), comprising:

laser generating means for generating repeating laser pulses;
selection means for selecting at least one sampling pulse from the repeating laser pulses to stroboscopically sample a waveform from the DUT;
counting means coupled to the selection means for counting the repeating laser pulses generated by the laser generating means;
trigger means for generating a trigger signal configured to control clocking of the DUT;
synchronizing means coupled to the switch, the trigger means, and the mode locked laser for synchronizing the repeating laser pulses with the trigger signal;
and
phase generation means coupled to the synchronizing means for generating a phase difference between the trigger signal and the repeating laser pulses;
wherein the laser synchronizing apparatus is configured to loop a test pattern to test the DUT, each loop of the test pattern taking M clocks to execute, M being an integer, the mode locked laser generating N pulses during each loop of the test pattern, N being an integer.

5 more elements

Dependencies are inferred from the claim text.

Method and apparatus for synchronizing a mode locked laser with a device under test

Life of this patent

Method and apparatus for synchronizing a mode locked laser with a device under test

Life of this patent

Abstract

Claims28