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3V CMOS Rail to Rail Op-AmpAbdelMoneim, K.M.; Mahmoud, S.A.;Microelectronics, 2007. ICM 2007. Internatonal Conference on29-31 Dec. 2007 Page(s):373 - 376 Digital Object Identifier 10.1109/ICM.2007.4497732

Student : ming-long chuangDate:10/05/2009

National Changhua University Department of Graduate Institute of Integrated Circuit Design

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Outline

Abstract INTRODUCTION RAIL TO RAIL INPUT STAGE WITH

CONSTANT RAIL TO RAIL OUTPUT STAGE SIMULATION RESULTS CONCLUSION

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Abstract A new CMOS Op-Amp that having a rail to rail o

peration is presented. The proposed Op-Amp has a constant gm at the input stage.

A cascode stage that achieves a gain greater than 100dB over almost full range of the common mode input voltage.

A common source configuration that increases the output swing between the rails.

A class AB control circuit is used to provide a stable biasing at the output stage.

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INTRODUCTION OP-AMPS are one of the most essential

analog building blocks for analog signal processing . One of its crucial advantages is its use in implementing continuous time filters that are used to convert the discrete manner of switched capacitor filters to analog manner.

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INTRODUCTION One of the main drawbacks of using Op-Amps u

nder low voltage is the degradation of its performance over the input range specially at the input stage where the transconductance “gm” is not constant over the entire common mode input voltage “VCM” resulting in stability problems.

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r to r input stage with constantGeneral Architecture

The complete input stage architecture with constant gmT.

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r to r input stage with constantGeneral Architecture

The transconductance “gm” of a MOS transistor at saturation is given by:

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r to r input stage with constantGeneral Architecture

If gmT is made constant over the entire common mode input voltage, a constant gm could be achieved and this will be done by manipulating the sum of tail currents of the differential pairs to be constant over the entire common mode input voltage.

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r to r input stage with constantgm-Equalizer Circuit

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r to r input stage with constantgm-Equalizer Circuit

Another advantage of this circuit is it’s independence on mismatches of the n-channel and p-channel transistors and thus gmT is kept constant although n p Kn≠ Kp which might be caused during the fabrication process.

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RAIL TO RAIL OUTPUT STAGE General Architecture The purpose of the output stage is to provide as

large gain as possible and to obtain an output that swings from rail to rail without distortion at high frequency signals.

The common source configuration acts as a buffer to the cascode stage and compensate for its large output resistance and provide the Op-Amp with low output resistance.

The class AB control circuit is used to avoid distortion.

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RAIL TO RAIL OUTPUT STAGE General Architecture

Output stage architecture

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RAIL TO RAIL OUTPUT STAGE Class AB Control Circuit

Complete output stage

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SIMULATION RESULTS

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SIMULATION RESULTS Complete CMOS Op-Amp

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Conclusions This paper introduced a new CMOS low voltage

rail to rail Op-Amp that has constant transconductance at the input stage over full range of common mode input voltage with more that 100dB gain without loss of stability.

The proposed Op-Amp has been confirmed using Pspice simulations.

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Thank you for your attention