Harmonic distortion on class AB CMOS current output stages

Linearity performance in class AB CMOS current output stages is discussed, and simplified equations are derived for the harmonic distortion. It was found that channel-length modulation and transistor mismatches are the main sources of distortion in current output stages. A novel high-performance class AB current output stage is also presented which is based on active-gain enhanced cascoded mirrors. It overcomes the nonlinearity caused by channel-length modulation and provides a very high output resistance. The linearity performance of the proposed circuit is only limited by the fundamental constraints due to transistor mismatches.