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Adaptive Averaging Circuit

IP.com Disclosure Number: IPCOM000091637D
Original Publication Date: 1968-Apr-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Related People

Jones, GD: AUTHOR [+2]

Abstract

This adaptive circuit measures incoming analog signals to determine when the integrated time average of the signal is less than a predetermined threshold level. Such a circuit is useful when processing signals transmitted over telephone lines where knowledge of the level of line noise is important for proper system operation. The adaptive characteristics of the circuit provide fast measurement of the time average of the incoming signals and the detection of the condition when the average reaches a predetermined level for a predetermined time. The circuit renders the averaging time an inverse function of the signal amplitude. Thus, low-level averages such as line noise can be detected precisely even after the occurrence of large amplitude signals such as speech.

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Adaptive Averaging Circuit

This adaptive circuit measures incoming analog signals to determine when the integrated time average of the signal is less than a predetermined threshold level. Such a circuit is useful when processing signals transmitted over telephone lines where knowledge of the level of line noise is important for proper system operation. The adaptive characteristics of the circuit provide fast measurement of the time average of the incoming signals and the detection of the condition when the average reaches a predetermined level for a predetermined time. The circuit renders the averaging time an inverse function of the signal amplitude. Thus, low-level averages such as line noise can be detected precisely even after the occurrence of large amplitude signals such as speech. This ability is not in fixed interval or linear time averaging circuits. The circuit measures the time period between successive accumulations to a predetermined level and this time period is qualified to a preset time limit.

An audio or speech signal is amplified and rectified before being applied to a voltage integrator. Output voltage E1 of the integrator is the product of the average of the signal during the integration period SA and the length of the period T. Signal E1 is compared with reference voltage ER in a voltage comparator. When E1 exceeds ER, the comparator changes states and fires a single-shot circuit. The latter resets the voltage integrator to zero to begin a new averaging period. The length of the averaging period is determined by the time taken for E1 to equal ER. The integration period is T = ER/SA. For a given ER, the value of SA is found by measurin...