A novel composite cell based, constant-gm, rail-to-rail CMOS input-stage

This paper reports on a novel circuit design technique for low-voltage rail-to-rail constant-g_m input-stages based on CMOS composite cells. To achieve rail-to-rail input swing, two pairs of this cell are connected in parallel. The transconductance of each pairs are inherently tunable by a biasing voltage. The constant-g_m characteristic is controlled by applying suitable values to these biasing voltages maintaining a smooth response over the change of input common mode voltage. HSPISE simulations show that the overall transconductance has linearity better than 6 percent with 2.5V supply voltage.