WIDE_BANDWIDTH_PEAK_DETECTOR

Published:2009/7/6 3:00:00 Author:May | From:SeekIC

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 VIN is a greater negative voltage than VOUT; 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 VOUT 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 R1. Reducing the value of C1 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 VOUT by 2 using two 1-KΩ resistors and feed the comparator VOUT/2 rather than VOUT.



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