3V CMOS Rail to Rail Op-Amp AbdelMoneim, K.M.; Mahmoud, S.A.; Microelectronics, 2007. ICM 2007. Internatonal Conference on 29-31 Dec. 2007 Page(s):373 - 376 Digital Object Identifier 10.1109/ICM.2007.4497732 Student : ming-long chuang Date:10/05/2009 National Changhua University Department of Graduate Institute of Integrated Circuit Design

Outline Abstract INTRODUCTION RAIL TO RAIL INPUT STAGE WITH CONSTANT RAIL TO RAIL OUTPUT STAGE SIMULATION RESULTS CONCLUSION

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

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.

INTRODUCTION One of the main drawbacks of using Op-Amps under 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.

r to r input stage with constant General Architecture The complete input stage architecture with constant gmT.

r to r input stage with constant General Architecture The transconductance “gm” of a MOS transistor at saturation is given by:

r to r input stage with constant General 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.

r to r input stage with constant gm-Equalizer Circuit

r to r input stage with constant gm-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.

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.

RAIL TO RAIL OUTPUT STAGE General Architecture Output stage architecture

RAIL TO RAIL OUTPUT STAGE Class AB Control Circuit Complete output stage

SIMULATION RESULTS

SIMULATION RESULTS Complete CMOS Op-Amp

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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