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**CMOS Operational Amplifiers (A Review)**

Data Converters CMOS Operational Amplifier Professor Y. Chiu EECT Fall 2014 CMOS Operational Amplifiers (A Review)

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**Data Converters CMOS Operational Amplifier Professor Y. Chiu**

EECT Fall 2014 Negative Feedback Closed-loop linearity is achieved by negative feedback with large loopgain Negative feedback reduces gain sensitivity and harmonic distortion

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**Folded-Cascode Op-Amp**

Data Converters CMOS Operational Amplifier Professor Y. Chiu EECT Fall 2014 Folded-Cascode Op-Amp Differential A0 ~ (gm·ro)2 ~ 40-50dB Vo,pp ~ 2(VDD-4VDSAT) Noise factor ~ 3 ωp2 ~ fT/3 Efficiency ~ 50% Load-compensated Flexible input CM 2VDSAT Vo 2VDSAT Most often used single-stage topology, easy to bias

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**2X more power-efficient than the folded-cascode topology, fast**

Data Converters CMOS Operational Amplifier Professor Y. Chiu EECT Fall 2014 Telescopic Op-Amp Differential A0 ~ (gm·ro)2 ~ 40-50dB Vo,pp ~ 2(VDD-5VDSAT) Noise factor ~ 2 ωp2 ~ fT/2 Efficiency ~ 100% Load-compensated Fixed input CM 2VDSAT Vo 3VDSAT 2X more power-efficient than the folded-cascode topology, fast

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**Not as power-efficient as single stage, suitable for low VDD**

Data Converters CMOS Operational Amplifier Professor Y. Chiu EECT Fall 2014 Two-Stage Op-Amp Differential A0 ~ (gm·ro)3 ~ 60-70dB Vo,pp ~ 2(VDD-3VDSAT) N2 = N1·β·CM/CL Noise factor ~ 2+2β ωp2 ~ gm2/CL Efficiency < 50% Miller-compensated Fixed input CM VDSAT Vo 2VDSAT Not as power-efficient as single stage, suitable for low VDD

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**Pseudo-Differential Op-Amp**

Data Converters CMOS Operational Amplifier Professor Y. Chiu EECT Fall 2014 Pseudo-Differential Op-Amp Differential A0 ~ (gm·ro)2 ~ 40-50dB Vo,pp ~ 2(VDD-4VDSAT) Noise factor ~ 2 ωp2 ~ fT/2 Efficiency ~ 100% Load-compensated Fixed input CM No CMFB point 2VDSAT Vo 2VDSAT As power-efficient and fast as telescopic, but Vocm is a problem

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**Data Converters CMOS Operational Amplifier Professor Y. Chiu**

EECT Fall 2014 CMOS Gain-Boosting A0 ~ Aa·(gm·ro)2 ~ dB, limited by substrate current Single-stage design, same output swing, suitable for SC circuits Auxiliary amplifiers introduce pole-zero doublet (slow settling), additional noise

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