Posted on Mar 14, 2013

This circuit can detect the positive peaks for signal frequencies higher than 5 MHz. It yields ±1% accuracy for 400 mV to 4 V pk-pk signal amplitudes on sine, square, and triangular waveforms. The Am685 comparator output increases whenever VrN is a greater negative voltage than Vour; the high comparator output, in turn, charges C1 in a positive direction. The CA3140 op amp amplifies the C1 voltage with respect to the ECL-switching-threshold voltage ( -1.3 V) developed by diodes D1 and D2. For repetitive waveforms, each cycle boosts Vaur until it equals the peak input value. The peak-detection process is aided by the comparator`s open-emitter output, which allows C1 to charge rapidly through R2, but to discharge slowly through R2 and Rl.

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Reducing the value of Cl shortens system-response times. Although the circuit can"t detect negative-going peaks, it can be modified to measure the pk-pk value of bipolar signals that are symmetric about ground. To do so, divide Vour by 2 using two 1-K!l resistors and feed the comparator Vour/2 rather than Vour.

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