chapter  8
88 Pages

- 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.