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AM STEREO CORRECTION BALANCE CIRCUIT

IP.com Disclosure Number: IPCOM000005587D
Original Publication Date: 1985-Oct-01
Included in the Prior Art Database: 2001-Oct-17
Document File: 1 page(s) / 49K

Publishing Venue

Motorola

Related People

Lawrence M. Ecklund: AUTHOR

Abstract

This circuit may be used to eliminate possible distortion introduced into the AM stereo signals by changes in the DC level of one or both of the envelope signal and the in-phase signal. Since these two signals are com- pared to produce the cosine correction signal, any change in the relative DC levels will introduce distortion since it will be interpreted by the correction circuit as an error requiring correction.

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m MOIOROLA Technical Developments Volume 5 October 1965

AM STEREO CORRECTION BALANCE CIRCUIT

by Lawrence M. Ecklund

   This circuit may be used to eliminate possible distortion introduced into the AM stereo signals by changes in the DC level of one or both of the envelope signal and the in-phase signal. Since these two signals are com- pared to produce the cosine correction signal, any change in the relative DC levels will introduce distortion since it will be interpreted by the correction circuit as an error requiring correction.

   A potentiometer circuit is included for making the initial adjustment, minimizing or removing any distortion due to different DC levels. The circuit is basically a current source which is coupled to source or sink current to the I detector circuit as required. The amount and direction of current are varied in resonse to the average of the DC at the output of a low pass filter connected to the Q detector terminal.

   An op amp circuit couples the filtered signal to the current source transistor and a feedback loop prevents error from being introduced into the source circuit. The current source is coupled to a current mirror which in- cludes the potentiometer circuit in one branch. When a current is sourced or sunk in the current source, a cor- responding current is sourced or sunk in the second mirror branch. The output of the second branch is coupled back to the I detector to balance the DC levels of the envelope and in-phase output signals....