A 1.5-V, Constant-Gm, Rail-to-Rail Input Stage Operational Amplifier

In this paper, a 1.5 V supply, rail-to-rail operational amplifier has been designed. Because of low voltage operation we have been made to use input differential pair in weak inversion mode and consequently low frequency response is natural. To obtain a gm-constant transconductor in first stage we use from a different structure that achieves smaller gm variation than previously defined circuits. A new CMFB circuit, also proposed, which is very efficient and suitable for low voltage operations. This opamp is designed in 0.35 mum CMOS process, and simulated in HSPICE.