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– 1 – Data ConvertersCMOS Operational AmplifierProfessor Y. Chiu EECT 7327Fall 2014 CMOS Operational Amplifiers (A Review)

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Negative Feedback – 2 – Data ConvertersCMOS Operational AmplifierProfessor Y. Chiu EECT 7327Fall 2014 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 – 3 – Data ConvertersCMOS Operational AmplifierProfessor Y. Chiu EECT 7327Fall 2014 Differential A 0 ~ (g m ·r o ) 2 ~ 40-50dB V o,pp ~ 2(V DD -4V DSAT ) Noise factor ~ 3 ω p2 ~ f T /3 Efficiency ~ 50% Load-compensated Flexible input CM Most often used single-stage topology, easy to bias 2V DSAT VoVo

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Telescopic Op-Amp – 4 – Data ConvertersCMOS Operational AmplifierProfessor Y. Chiu EECT 7327Fall 2014 Differential A 0 ~ (g m ·r o ) 2 ~ 40-50dB V o,pp ~ 2(V DD -5V DSAT ) Noise factor ~ 2 ω p2 ~ f T /2 Efficiency ~ 100% Load-compensated Fixed input CM 2X more power-efficient than the folded-cascode topology, fast 2V DSAT 3V DSAT VoVo

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Two-Stage Op-Amp – 5 – Data ConvertersCMOS Operational AmplifierProfessor Y. Chiu EECT 7327Fall 2014 Differential A 0 ~ (g m ·r o ) 3 ~ 60-70dB V o,pp ~ 2(V DD -3V DSAT ) N 2 = N 1 ·β·C M /C L Noise factor ~ 2+2β ω p2 ~ g m2 /C L Efficiency < 50% Miller-compensated Fixed input CM Not as power-efficient as single stage, suitable for low V DD V DSAT 2V DSAT VoVo

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Pseudo-Differential Op-Amp – 6 – Data ConvertersCMOS Operational AmplifierProfessor Y. Chiu EECT 7327Fall 2014 Differential A 0 ~ (g m ·r o ) 2 ~ 40-50dB V o,pp ~ 2(V DD -4V DSAT ) Noise factor ~ 2 ω p2 ~ f T /2 Efficiency ~ 100% Load-compensated Fixed input CM No CMFB point As power-efficient and fast as telescopic, but V ocm is a problem 2V DSAT VoVo

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CMOS Gain-Boosting – 7 – Data ConvertersCMOS Operational AmplifierProfessor Y. Chiu EECT 7327Fall 2014 A 0 ~ A a ·(g m ·r o ) 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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