2.1 The bipolar OTA
The most simple bipolar OTA consists of a differential pair to convert the input voltage difference
to two currents I+ and I−. These two currents are then mirrored to the output so that their
difference becomes the output of the OTA, while the rest of the OTA is made up of bias circuitry.
The truly great feature of this “long-tailed differential pair” as it is often called is that the tail
current, which is a necessary part of the biasing, can be used to control the transconductance as
we will see in a moment.