Thermal hotspot (THS) fault isolation is an effective technique for detecting heat-generating failure modes, especially those involving excessive current or resistance. The normal approach for modulation mode THS analysis is to connect a power supply to the leakage pin of the device under test through the modulation switch on the instrument. There are instances, however, where this may not work. This paper discusses two such cases: one in which the output terminal of the modulation switch is connected to the failing device through a series resistor in order to limit current, and one where a voltage divider is used to connect the unit under test to the modulation switch in order to create ramping sequences that mimic IQ current spikes for THS analysis.

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