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Adjustable Dial Pulse Clipper

IP.com Disclosure Number: IPCOM000085397D
Original Publication Date: 1976-Apr-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 21K

Publishing Venue

IBM

Related People

Dooley, TE: AUTHOR

Abstract

Positive and negative peaks of high-voltage dial pulses normally present in an audio channel of a dial pulse controlled dictation system, are clipped without affecting channel gain.

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Adjustable Dial Pulse Clipper

Positive and negative peaks of high-voltage dial pulses normally present in an audio channel of a dial pulse controlled dictation system, are clipped without affecting channel gain.

High-voltage dial pulses exceeding 8 volts peak are present on the audio channel where audio signals are in the range of 0.8 VRMS maximum. These high-voltage positive and negative pulses can adversely affect system audio circuits where the recorder incorporates a voltage input controlled automatic gain control (AGC) circuit. The effect of these dial pulses on the AGC can be minimized by clipping. The audio input level to the system from the telephone line may vary over a 40 db range, depending on the PBX in use, and therefore the clipping circuit must be adjustable at the system installation.

The clipping level is adjusted by variable resistor R1. The output voltage Vx of the differential input operational amplifier will clip on the positive side as a function of +Vs, and the negative side as a function of -Vs. For this application, +Vs nominally equals -Vs for symmetrical clipping.

The gain (Vx/Vin) = (R1 + R2)/R2 is adjusted by varying resistor R1, such that the highest level audio signal for the particular PBX in use is just below the clipping level of the operational amplifier. This adjustment does not change the relationship Vout equals Vin. Therefore, this adjustment does not alter the channel with respect to audio signals when Vin is below the adju...