A new SMC compensation strategy for three stage amplifiers based on differential feedback path

摘要

A new single Miller Capacitor frequency compensation scheme for three stage amplifier is proposed. In conventional three-stage amplifier a differential feedback, from output of the second and the third stage is added to output of the first stage, which significantly improves Phase Margin and decreases compensation capacitor to less than 2% of the load capacitor value. Analyses show that the stability can be perfectly ensured. A three-stage amplifier has been simulated with and without a differential feedback in a 0.18μm CMOS. The proposed amplifier driving a 100pF capacitance load, achieved 1.39MHz gain-bandwidth product and 90° Phase Margin with a 1.8V supply. An amplifier based on conventional nested Miller compensation (NMC) can just achieve less than 0.23MHz GBW with the same load, while using more than 100pF as compensation capacitor. So this method shows an improvement of a factor of 6 in GBW and reduction of a factor of 50 in the size of compensation capacitor. It is a suitable strategy for ON-CHIP compensation in comparison to other methods.