High-linearity low-voltage self-cascode class AB CMOS current output stage

A novel cascode current mirror structure is proposed, which is suitable for use in low-voltage current output stages. The current mirror makes use of the self-cascode structure and partial positive-feedback to reduce the input and output voltage restrictions. ALI devices are aimed to be kept in saturation to achieve a high output impedance. Besides known ones, further possibilities are investigated to keep all devices in saturation. It is also shown that, to enhance the output impedance, the regulated cascode scheme can be adopted with minimum number of additional devices, without degrading the mirroring accuracy. A class AB CMOS current output stage employing the proposed current mirrors is simulated with PSpice so as to verify the mentioned performance characteristics.