Input common-mode voltage behaviour of CMOS bulk-driven differential stages

In this paper, the response of a bulk-driven MOS input stage is discussed and experimentally evaluated over the entire input common-mode voltage range. In particular, the behavior of the effective input transconductance and the input current is studied for different gate bias voltage conditions of the input transistors. A simple technique to automatically control the gate bias voltage of a bulk-driven differential pair is also presented so as to optimize the design tradeoff between the effective input transconductance and the input current. Experimental results, in standard 0.35-mum CMOS technology, validate the effectiveness of the proposed technique.