Data Converters EECT 7327 CMOS Operational Amplifier Fall
- Slides: 7
Data Converters EECT 7327 CMOS Operational Amplifier Fall 2014 Professor Y. Chiu CMOS Operational Amplifiers (A Review) – 1–
Data Converters EECT 7327 CMOS Operational Amplifier Fall 2014 Professor Y. Chiu Negative Feedback • Closed-loop linearity is achieved by negative feedback with large loopgain • Negative feedback reduces gain sensitivity and harmonic distortion – 2–
Data Converters EECT 7327 CMOS Operational Amplifier Fall 2014 Professor Y. Chiu Folded-Cascode Op-Amp • Differential 2 VDSAT • A 0 ~ (gm·ro)2 ~ 40 -50 d. B • Vo, pp ~ 2(VDD-4 VDSAT) • Noise factor ~ 3 Vo • ωp 2 ~ f. T/3 • Efficiency ~ 50% 2 VDSAT • Load-compensated • Flexible input CM Most often used single-stage topology, easy to bias – 3–
Data Converters EECT 7327 CMOS Operational Amplifier Fall 2014 Professor Y. Chiu Telescopic Op-Amp 2 VDSAT • Differential • A 0 ~ (gm·ro)2 ~ 40 -50 d. B • Vo, pp ~ 2(VDD-5 VDSAT) Vo • Noise factor ~ 2 • ωp 2 ~ f. T/2 • Efficiency ~ 100% 3 VDSAT • Load-compensated • Fixed input CM 2 X more power-efficient than the folded-cascode topology, fast – 4–
Data Converters EECT 7327 CMOS Operational Amplifier Fall 2014 Professor Y. Chiu Two-Stage Op-Amp • Differential VDSAT • A 0 ~ (gm·ro)3 ~ 60 -70 d. B • Vo, pp ~ 2(VDD-3 VDSAT) Vo • N 2 = N 1·β·CM/CL • Noise factor ~ 2+2β • ωp 2 ~ gm 2/CL 2 VDSAT • Efficiency < 50% • Miller-compensated • Fixed input CM Not as power-efficient as single stage, suitable for low VDD – 5–
Data Converters EECT 7327 CMOS Operational Amplifier Fall 2014 Professor Y. Chiu Pseudo-Differential Op-Amp • Differential 2 VDSAT • A 0 ~ (gm·ro)2 ~ 40 -50 d. B • Vo, pp ~ 2(VDD-4 VDSAT) • Noise factor ~ 2 Vo • ωp 2 ~ f. T/2 • Efficiency ~ 100% • Load-compensated 2 VDSAT • Fixed input CM • No CMFB point As power-efficient and fast as telescopic, but Vocm is a problem – 6–
Data Converters EECT 7327 CMOS Operational Amplifier Fall 2014 Professor Y. Chiu CMOS Gain-Boosting • A 0 ~ Aa·(gm·ro)2 ~ 60 -100 d. B, limited by substrate current • Single-stage design, same output swing, suitable for SC circuits • Auxiliary amplifiers introduce pole-zero doublet (slow settling), additional noise – 7–
