Waveform mapping and gated laser voltage imaging

A system for testing a circuit, comprising:

• a test-loop generator configured to supply a test-loop signal to the circuit, wherein the test-loop signal comprises a stimulus signal that repeats every test-loop period;
• a laser source;
• first optics configured to direct a laser beam from the laser source onto the circuit;
• a sensor configured to detect reflected laser light from the circuit and to generate a sensor output in response thereto;
• a high-speed digital signal averager configured to generate a digital output signal based on the sensor output and a synchronization signal;
• and
• a gate-generator circuit electrically coupled to the high-speed signal averager and configured to output a gate signal having a gate start time and a gate duration, wherein the duration is less than the test-loop period.

A diagnostic measurement method, comprising:

• stimulating a device under test with a test pattern, the test pattern comprising a stimulus signal that repeats every test-loop period;
• illuminating an area of the device under test with a laser beam in a raster scan;
• detecting light reflecting off the device under test in response to the illuminating;
• identifying a direct-current (DC) component and an alternating-current (AC) component of the detected reflected light;
• averaging the AC component over a plurality test-loop periods based on a trigger signal and a gate signal, wherein the trigger signal synchronizes the AC component to the test pattern and during each test-loop period the gate signal selects a portion of the AC component corresponding to a time that is less than the test-loop period to be averaged;
• digitizing the averaged AC component to generate an output signal;
• and
• storing the output signal in a memory.