- Transistor-Level Front-End Design
In this chapter we focus on the transistor-level implementation of front-end amplifiers,
deriving guidelines for topology choice and transistor sizing. Most systems use as the
input stage a singled ended cascode amplifier with a transimpedance feedback loop.
As it was introduced in the previous chapters, the term “Charge Sensitive Amplifier”
(CSA) is rigorously correct only if the feedback time constant is large enough that
it does not contribute significantly to the overall signal shaping performed by the
front-end. The optimization rules reported here are nevertheless valid also when the
feedback resistor has a primary role in the signal processing, i.e. when it would be
more appropriate to speak of a “transimpedance configuration” in the strict sense. In
the following, we therefore use the word CSA to indicate any input stage based on a
high-gain voltage amplifier supplemented with feedback.