A programmable gain low noise amplifier includes a tail current transistor
(Q3) having a source coupled to a first reference voltage (VDD) and a
drain coupled to a tail current conductor (18) and, in a differential
input embodiment, a plurality of pairs (Q4,5, Q7,8, Q10,11, Q13,14) of
differentially coupled input transistors. Each pair includes a first
input transistor having a gate coupled to a first input conductor (19A)
and a drain coupled to a first output conductor (26A) and a second input
transistor having a gate coupled to a second input conductor (19B), a
source coupled to a source of the first transistor, and a drain coupled
to a second output conductor (26B). The sources of the first and second
input transistors of some or all of the pairs are selectively coupled to
the tail current conductor (18) in it response to corresponding gain
control signals (B1,2,3).