Step gain-variable CMOS amplifier

A step gain-variable CMOS amplifier includes an input pair of transistors, a bias current generator connected between a common source node of the input pair of transistors and a ground node, and a pair of load transistors. The pair of load transistors is connected between a supply voltage node and, respectively, to the drain nodes of the input pair of transistors. The CMOS amplifier includes a plurality of second input pairs of transistors to be connected in parallel to the input pair of transistors for increasing the effective width of the resultant transistors. Alternativelty, the CMOS amplifier includes a plurality of second load pairs of transistors to be connected in parallel to the load pair of transistors for increasing the effective width of the resultant transistors. Pairs of path selection switches may be programmably closed for connecting in parallel the selected pairs of transistors.