A high-speed CMOS amplifier with dynamic frequency compensation

High-performance CMOS operational amplifiers with advanced frequency compensation, dynamic biasing, and enhanced slew rate are presented. Prototyping amplifiers with three design techniques have been fabricated by the MOSIS service using a 2- mu m scalable CMOS technology. Experimental results show a significant speed-up on amplifier transient responses. The dynamic biasing technique is used to enhance the slew rate by increasing the bias current of the input differential pair when the differential-mode input voltage is large. Another differential pair is added to sense the input voltage. The additional circuitry increases the input capacitance of an MOS amplifier, which can degrade power supply rejection ratio characteristics. Since the slew rate enhancement factor is proportional to the ratio of bias current and additional dynamic biasing current, a large improvement on slew rate always generates additional ripples on the power lines.<
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