Browse Prior Art Database

Envelope Demodulator

IP.com Disclosure Number: IPCOM000095568D
Original Publication Date: 1964-Mar-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Comer, DJ: AUTHOR [+3]

Abstract

This circuit detects the amplitudes of consecutive peaks of an AC signal and provides a DC output voltage indicative of the last peak detected. In this manner, the circuit demodulates the envelope of the AC signal accurately and has a fast response time.

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Envelope Demodulator

This circuit detects the amplitudes of consecutive peaks of an AC signal and provides a DC output voltage indicative of the last peak detected. In this manner, the circuit demodulates the envelope of the AC signal accurately and has a fast response time.

The AC input signal 10 is applied across a first capacitor 11. This charges to the first peak value of the input wave. Grounding switch 12 is closed periodically, discharging capacitor 11. Switch 12 is opened immediately after having been closed, but unless the input happens to be positive at the time, the output remains at ground potential. When the input wave goes positive, the output again follows. Transistor 13 transmits the output of capacitor 11 to a second capacitor 14 and a second grounding switch 15 and resistor 16.

Capacitor 14 now charges to the voltage of capacitor 11, but when capacitor 1 1 is discharged, the second remains charged. Switch 15 is closed sometime after the first is reopened. Capacitor 14 discharges through the resistor 16 towards ground, but when it reaches the new voltage of capacitor 11, transistor 13 becomes forwardly-biased, holding the emitter at such voltage due to the current through the resistor Thus, the output of the second stage approximately follows the peak voltages of the input signal, but is much smoother than the first stage since it is not periodically, fully discharged to ground.

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