CMOS low-voltage rail-to-rail V-I converter

A low-voltage rail-to-rail voltage/current-controlled voltage-to-current converter, which is first order insensitive to the threshold voltage variation, is introduced. This circuit can be used as a basic building block to construct low-voltage current-mode analog computational circuits, which can perform functions such as square-rooting, squaring, multiplication, sum of squares, difference of squares and etc. First, a low-voltage N-type V-I converter cell is presented. A complementary P-type V-I converter is used in parallel with the N-type V-I converter to achieve common-mode rail-to-rail operation. Moreover, to achieve a constant transconductance of the V-I converter, P-type and N-type bias control circuits are utilized to provide bias currents. Finally, SPICE simulations results are given. The variation of the transconductance is shown to be less than 5%