Quasi-peak

A quasi-peak detector is a type of electronic detector or rectifier. Quasi-peak detectors for specific purposes have usually been standardized with mathematically precisely defined dynamic characteristics of attack time, integration time, and decay time or fall-back time.

Quasi-peak detectors play an important role in electromagnetic compatibility (EMC) testing of electronic equipment, where allowed levels of electromagnetic interference (EMI), also called radio frequency interference (RFI), are given with reference to measurement by a specified quasi-peak detector. This was originally done because the quasi-peak detector was believed to better indicate the subjective annoyance level experienced by a listener hearing impulsive interference to an AM radio station. Over time standards incorporating quasi-peak detectors as the measurement device were extended to frequencies up to 1 GHz, although there may not be any justification beyond previous practice for using the quasi-peak detector to measure interference to signals other than AM radio. The quasi-peak detector parameters to be used for EMC testing vary with frequency . Both CISPR and the U.S. Federal Communications Commission (FCC) limit EMI at frequencies above 1 GHz with reference to an average-power detector, rather than quasi-peak detector.

Conceptually, a quasi-peak detector for EMC testing works like a peak detector followed by a lossy integrator. A voltage impulse entering a narrow-band receiver produces a short-duration burst oscillating at the receiver center frequency. The peak detector is a rectifier followed by a low-pass filter to extract a baseband signal consisting of the slowly (relative to the receiver center frequency) time-varying amplitude of the impulsive oscillation. The following lossy integrator has a rapid rise time and longer fall time, so the measured output for a sequence of impulses is higher when the pulse repetition rate is higher. The quasi-peak detector is calibrated to produce the same output level as a peak-power detector when the input is a continuous wave tone .

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