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A TWO STAGE TEMPERATURE INDEPENDENT AUDIO LIMITER

IP.com Disclosure Number: IPCOM000005428D
Original Publication Date: 1980-Aug-01
Included in the Prior Art Database: 2001-Oct-10
Document File: 2 page(s) / 88K

Publishing Venue

Motorola

Related People

Jerry Miller: AUTHOR

Abstract

A method of obtaining temperature independence in an audio limiter is described. Low cost is main- tained by not using temperature sensing devices such as thermistors. Only resistors and the low cost MLM324 quad op-amp are used. The implementation described uses a single 4-volt supply.

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MOTOROLA Technical Disclosure Bulletln Vol. 1 No. 1 August 1966

A TWO STAGE TEMPERATURE INDEPENDENT AUDIO LIMITER By Jerry Miller

ABSTRACT

   A method of obtaining temperature independence in an audio limiter is described. Low cost is main- tained by not using temperature sensing devices such as thermistors. Only resistors and the low cost MLM324 quad op-amp are used. The implementation described uses a single 4-volt supply.

INTRODUCTION

   The MLM324 family of operational amplifiers may be used as limiters simply by allowing the amplifier to limit against its supply rails. The upper and lower supply rails are the voltage levels at which the output saturates when the amplifier is in limiting. However, the peak-to-peak amplitude of the limited output can vary by as much as 0.5 V from -30°C to +6O'C. This is due primarily to the upper rail's variation over temperature. The lower rail comes within about 50 mV of ground (when operated from a single negative ground supply) and is very consistent ( - & 15 mV) with temperature changes from -30% to + 60°C. By utilizing only this lower rail to perform all limiting, a very temperature stable output results. In addition, the limiter is very low cost due to the use of only resistors and the low cost MLM324 op-amps. Presumably, there are other op-amp families with similar characteristics which can be utilized in the same manner.

SYSTEM AND CIRCUIT DESCRIPTION

   A block diagram of the limiter system is shown in Figure 1. The first stage amplifier provides the desired amount of gain. It can either be inverting or non-inverting as desired. It is biased (as is the second stage), such that the quiescent DC output is somewhat closer to ground than to the worst case upper rail voltage over temperature. Therefore, the output of the first stage begins limiting at the lower rail...