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Variable-Gain Current Conveyor-Based Instrumentation Amplifier with Differential Outputs

IP.com Disclosure Number: IPCOM000245339D
Publication Date: 2016-Mar-02
Document File: 7 page(s) / 226K

Publishing Venue

The IP.com Prior Art Database

Abstract

CMOS transmission gate switches when used in instrumentation amplifiers introduce distortions at undesirable levels. The magnitude of the on-resistance of these switches, which varies non-linearly with various influential factors, have to be controlled to ensure lower distortion levels. This paper describes a variable-gain current conveyer-based instrumentation amplifier with differential outputs, which does not introduce transmission gate distortion. Various gain control configurations of Dual-Output Transconductance Amplifier (DOTA) and Triple-Output Transconductance Amplifier (TOTA) based instrumentation amplifiers are discussed.

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Variable-Gain Current Conveyor-Based Instrumentation Amplifier with Differential Outputs

Paul M Werking

ABSTRACT

CMOS transmission gate switches when used in instrumentation amplifiers introduce distortions at undesirable levels. The magnitude of the on-resistance of these switches, which varies non-linearly with various influential factors, have to be controlled to ensure lower distortion levels. This paper describes a variable-gain current conveyer-based instrumentation amplifier with differential outputs, which does not introduce transmission gate distortion. Various gain control configurations of Dual-Output Transconductance Amplifier (DOTA) and Triple-Output Transconductance Amplifier (TOTA) based instrumentation amplifiers are discussed.


1. INTRODUCTION

Programmable Gain Instrumentation Amplifiers (PGIA) are Instrumentation Amplifiers (IA) with digitally programmable gains. Common applications of programmable gain amplifiers are motor control, signal and sensor conditioning, bar code readers and digital cameras. They can also be used for Analog-to-Digital Converter (ADC) driver applications, multiplexed analog applications, data acquisition, industrial and medical instrumentation. PGIAs with differential outputs such as PGA280 are also available in the market. They are of great utility since they are compatible with most popular ADCs having differential inputs.

CMOS transmission gate switches when used in an IA cause a significant amount of undesirable distortion. They have theoretically infinite off-resistance and on-resistance typically between 50 and 5000 ohms which is dependent on the process, supply voltage and temperature. The magnitude of this non-linear variation in resistance is significant and must be controlled in circuits where the amount of signal distortion is a concerning factor. This introduces the need for PGIAs which do not introduce transmission gate distortions at an undesirable level.

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2. EXISTING SOLUTION - VARIABLE GAIN CURRENT CONVEYER-BASED IA WITH SINGLE- ENDED OUTPUT

The existing technology which addresses the IA distortion problem is a variable gain current conveyer-based IA with single-ended output. This variable gain IA configuration includes a current conveyer AR1 which receives the first input voltage V1 and a second current conveyer AR2 which receives the second input voltage V2. A resistive element R1 is connected between the two current conveyers. Further, an amplifier is connected to the second current conveyer at its inverting input and a second resistive element R2 connects the second current conveyer and the inverting input of the amplifier to the output of the amplifier. Figure1 shows the configuration of a current conveyer-based IA, where the current conveyers illustrated are Dual-Output Transconductance Amplifiers (DOTA)

The gain of the IA in figure 1 can be made variable by replacing the resistive element R1 or the feedback resistor R2 or both with potentiometers (as...