Abstract: This paper presents a three-stage CMOS operational amplifier (opamp) that combines accuracy with stability for a wide range of capacitive loads.A so-called quenching capacitor is added to a multipath nested Miller compensation (MNMC) topology to obtain stability for a wide range of capacitive loads.Theoretical analysis and mathematical formulas are provided to prove the improvement in stability.A prototype of this frequency compensation scheme is implemented in a 0.7μm CMOS process.Measurements show that the amplifier can drive capacitive loads ranging from 100pF to 100μF with a gain of 90dB and a minimum phase margin of 26°.The amplifier has a unity-gain bandwidth of 1MHz for a 100pF capacitive load.It employs a quenching capacitance of 18pF.

Key words: operational amplifier, frequency compensation, phase margin, capacitive loads