EMC Question of the Week: March 16, 2020
The third harmonic of a continuous clock signal shows up as a narrow band peak in a conducted emissions measurement. How does the value measured with an average detector compare to the value measured with a peak detector?
- 3 dB higher
- 3 dB lower
- 13 dB lower
- the same
Answer
The correct answer is "d". For continuous signals, the peak value and the quasi-peak value and the average value are the same. The values will only be different for pulsed or modulated signals.
The value recorded by a peak detector is the not the peak amplitude of the signal in the time domain. It is the peak value of the average power recorded while the detector was dwelling in a given frequency band. The average detector output is essentially the average value of the average power recorded while the detector was dwelling in a given frequency band. If the power is constant during the measurement, the peak and average values are the same.
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