A CMOS rail-to-rail linear VI-converter

A linear CMOS VI-converter operating in strong inversion with a common-mode input range from the negative to the positive supply rail is presented. The circuit consists of three linear VI-converters based on the difference of squares principle. Two of these perform the actual V to I conversion, while the third changes the bias currents of the first two in response to changes in the input common-mode level. The resulting circuit has a large signal transconductance which is constant to within 3% over the entire common-mode input range. It can operate from a single supply voltage of 2.2 volts