The output common-mode voltage in multistage fully differential opamps can be set by using a single common-mode feedback loop around all stages or by independent loops for each stage. The two schemes are analyzed for their impact on the slew rate in a two-stage Miller-compensated class-A opamp. Analysis and simulation results show that using local common-mode feedback loops will lead to higher slew rate. This is because, when slewing, both upper and lower transistors receive signal dependent gate voltages with local common-mode feedback, making the behavior similar to that of a class-AB output stage. Also, with local common-mode feedback, the positive and negative slew rates are symmetric. © 2015 IEEE.

Nagendra Krishnapura

Department of Electrical Engineering

Amplifiers (electronic)

Analog integrated circuits

Differential amplifiers

Embedded systems

Operational amplifiers

power amplifiers

Analysis and simulation

Common mode feedback

Common mode voltage

Fully differential

INDEPENDENT LOOPS

LOCAL COMMON-MODE FEEDBACKS

OUTPUT STAGES

SLEW RATE ENHANCEMENT

FEEDBACK AMPLIFIERS

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IIT Madras

On Slew Rate Enhancement in Class-A Opamps Using Local Common-Mode Feedback

Proceedings of the IEEE International Conference on VLSI Design

A low-distortion active filter is realized using current-efficient feedforward-compensated operational amplifiers in the integrators and feedforward current injection in the summing amplifier. A third-order elliptic low-pass filter with two possible bandwidth settings of 17 and 8.5 MHz consumes 1.8 mW from a 1.8-V supply and occupies 0.17 μm2 in a 0.18- μm CMOS process. The measured maximum signal-to-noise and distortion ratios at the two bandwidth settings are 50.5 and 52.5 dB, respectively. The corresponding third-order intermodulation intercept points (IIP3) are +28.2 and +30.8 dBm. Automatic tuning is used at the startup to counter process variations and set the bandwidth accurately. © 2011 IEEE.

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Journal	Data powered by TypesetProceedings of the IEEE International Conference on VLSI Design
Publisher	Data powered by TypesetIEEE Computer Society
ISSN	10639667
Open Access	No