Peak Detector - Keysight X Series Measurement Manual

Detectors Used in EMI Measurements

Peak Detector

Peak Detector
Initial EMI measurements are made using the peak detector. This mode is much
faster than quasi-peak, or average modes of detection. Signals are normally
displayed on spectrum analyzers or EMC analyzers in peak mode. Since signals
measured in peak detection mode always have amplitude values equal to or higher
than quasi-peak or average detection modes, it is a very easy process to take a sweep
and compare the results to a limit line. If all signals fall below the limit, then the
product passes and no further testing is needed.
Peak detector operation
The EMI Receiver has an envelope or peak detector in the IF chain that has a time
constant, such that the voltage at the detector output follows the peak value of the IF
signal at all times. In other words, the detector can follow the fastest possible
changes in the envelope of the IF signal, but not the instantaneous value of the IF
sine wave.
Peak detector diagram
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