design and analysis of operationl trans conductance amplifier

7/31/2019 Design and Analysis of Operationl Trans Conductance Amplifier

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DESIGN AND ANALYSISOF OPERATIONLTRANSCONDUCTANCEAMPLIFIER

MEENAKSHI YADAVMVLSI-258-2K10M.Tech


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abstract

The outside world is actually of analognature and to be able to interact withcomputrs etc. we need some analog and mixanalog/digital circuits. Among various analogcircuits operational amplifier has a verydominant role. It is used in almost all analogapplications. Its main characterstics are highinput resistance, low output resistance, highgain , high CMRR, high unity gain bandwidth,and high common mode range (CMR) .Performance of any analog applicationdepends on these characterstics if they meetthe desired specification. Once the topology


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OUTLINE

INTRODUCTION

OPERATIONAL AMPLIFIER

OPERATIONAL TRANSCONDUCTANCEAMPLIFIER

PARAMETERS STUDIED

FOLDED CASCODE OTA

DESIGN PROCEDURE

TELESCOPIC OTA

DESIGN PROCEDURE


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OPERATIONAL AMPLIFIER

Basic building block in analog circuits.

Voltage controlled voltage source.

Low output impedance.

High differential input impedance.

High gain

Always used with external feedback circuitto create amplifier, filter , integretingcircuits.


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OPERATIONAL TRANSCONDUCTANCEAMPLIFIER

Voltage controlled current source.

High differential gain.

High output impedance.

Used without external feedback .

Has better frequency capability.

Transconductance (Gm) is the importantparameter.


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FOLDED CASCODE OTA

It is cascade of a differentialtransconductance stage with a current stagefollowed by a cascade current-mirror load

This op-amp uses cascading in output stagecombined with an unusual implementation of the differential amplifier to achieve goodinput common mode range.

Use of a cascade mirror leads to achieve thegain of two-stage and allows for self -compensation.


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DESIGN PROCEDURE


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w/l ratios after calculation

W/L ratio for1.25um technology

W/L ratio for 0.18um

technology


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Dc gain and unity gain b/w


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Phase margin


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Slew rate


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Input/output swing


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psrr


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Output offset


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results


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Telescopic OTA

The transistors are placed one on the top of the other to create a sort of Telescopiccomposition (this led to the circuit name astelescopic op-amp).

The input differential pair injects the signalcurrents into common gate stages.

The circuit achieves the differential to singleended conversion with a cascode currentmirror.

The small signal resistance at the outputnode is quite high; it is the parallel

connection of two cascode configurations.


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DESIGN PROCEDURE


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w/l ratios after calculation

W/L RATIO FOR 1.25UM TECHNOLOGY

W/L RATIO FOR 0.18UM TECHNOLOGY


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DC gain and unity gain b/w


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Phase margin


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Slew rate


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Input output swing


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Common mode gain


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RESULTS


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CONCLUSION

Operational transconductance amplifier is avoltage controlled current source.

It has a high differential input impedance

and high output impedance take at acapacitive load.

It is a open loop amplifier therefore usedwithout external feedback thereby havingbetter frequency capability.The important parameter of OTA is itstransconductance.

Telescopic OTA has higher speed and lesser


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Future scope

Folded cascade OTA and telescopic OTA if designed for a specific Gm value it is used toimplement active filter component such asresistor, inductors which are further used toimplement active filter such as butterworthfilter chebwyshev filter Bessel filter andelliptical filters.

These filters are are used in widebandapplication .


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refrences

1. Kuen-Jong Lee, Wei-Chiang Wang, andKou-Shung Huang, A Current-Mode TestableDesign of Operational TransconductanceAmplifierCapacitor Filters, IEEETransactions on Circuits and SystemsII:Analog And Digital Signal Processing, vol.46, no. 4, April 1999.

2. L. Weinberg, Network Analysis andSynthesis, New York, McGraw-Hill, 1962.


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design and analysis of operationl trans conductance amplifier

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