High-gain microwatt composite cascode op amps

This article discusses the composite cascode stage, both single-ended and differential, operating in the weak inversion or moderate inversion region. The gain of the MOS composite cascode differential stage can exceed 100,000?V/V, a figure that has never been reported in the literature. For low-frequency applications, this configuration can be used to fabricate op amps that have high-gain, low-power and low-nonlinear distortion. Two different architectures, both having two gain stages are reported. The first op amp uses the Widlar architecture to achieve a gain of 117?dB, a power dissipation of 110?µW and uses a compensation capacitor of only 3.5?pF. The second op amp uses a class AB stage for the second and final stage and utilises the parasitic capacitance at the output of the first stage for compensation. This self-compensating op amp has a gain of 110?dB and a power dissipation of 21?µW.