Browse Prior Art Database

HARDWARE ONLY SAMPLE AND HOLD AUTOMATIC LEVEL CONTROL WITH INFINITE HOLD TIME

IP.com Disclosure Number: IPCOM000007760D
Original Publication Date: 1996-Aug-01
Included in the Prior Art Database: 2002-Apr-19
Document File: 3 page(s) / 101K

Publishing Venue

Motorola

Related People

Douglas W. Eaton: AUTHOR

Abstract

This works good and can be implemented with very little circuitry. Unfortunately, even low leakage capac- itors and high input impedance Op-Amps cannot hold the charge for extended periods of time. Even several minutes is beyond the reach ofthese circuits.

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Technical Developments

HARDWARE ONLY SAMPLE AND HOLD AUTOMATIC LEVEL CONTROL WITH INFINITE HOLD TIME

by Douglas W. Eaton

INTRODUCTION

This works good and can be implemented with very little circuitry. Unfortunately, even low leakage capac- itors and high input impedance Op-Amps cannot hold the charge for extended periods of time. Even several minutes is beyond the reach ofthese circuits.

  With the advent of microprocessor controlled sys- tems, the limitations were overcome, but the cir- cuits became more complex. This added complex- ity brought added expense.

  Imagine yourself in the back of a speeding ambu- lance. As a paramedic, the life of the patient is in your hands as you race towards the hospital. As you transmit EKG data to a waiting doctor, the audio fades out, and the EKG data is interrupted. Although it is possible to re-establish contact by re-keying the radio, precious moments have been lost due to lim- ited "ALC hold time!'

  This paper describes a circuit that extends ALC hold time indefinitely. It can maintain the gain set- ting through a power loss, and requires only three ICs and fifteen passive components. This provides a cost and performance effective building block to the circuit designer. It would be very useful in applica- tions such as Tone Remote Control (where the sys- tem gain is set by Guard Tone) or Receiver Voting Systems (where the system gain is set by Status Tone). Both of these applications have suffered perform- ance problems due to the hold time limitations of capacitor hold circuits.

THE SOLUTION

  The following design is a low-cost, hardware only solution to the problem. The gain can be controlled by an EEPOT allowing the gain to be stor...