Many single-supply operational amplifiers are capable of rail-
to-rail input operation, if they have the proper input circuitry
to support this function. This article is an expansion of the
blog post “What does ‘rail to rail’ input operation really mean?
” By examining an additional input-stage topology and
implementing these op amps into some common op-amp circuits, you
will see what I mean. The article discusses a composite input-
stage topology for single-supply op amps. You may recall that
this topology exhibited an offset-voltage, crossover distortion
as the input common-mode voltage traveled across the full rail-
to-rail input voltage range. Switching from one differential
input stage to the other causes this distortion. Revisiting
single-supply input topologies The CMRR (common-mode rejection
ratio) specification describes changes in the amplifier’s
offset-voltage versus common-mode input changes. The
specification conditions can subtly describe the amplifier’s
rail-to-rail input topology. A typical commo