Integrated Source Follower for the Read-Out of Silicon Sensor Arrays

The Source Follower (SF) as the first amplification stage of the front-end electronics has proven to be an effective tool for low-noise read-out of silicon radiation sensors. Since the noise properties of a well-designed amplification circuit are mainly determined by its very first stage, constraints on the subsequent electronics are relaxed. Moreover, since the SF is characterized by a low output resistance, once it is completely integrated into the detector substrate, the connections to the out-of-chip part of the circuit are also relaxed. The effectiveness of this solution and the overall performance of the system depend on the sensor properties. In this paper, by presenting analytical calculations and measurements, we identify the sensor types that could profit from the advantages provided by the integrated SF, and the devices where the SF shows some pitfalls. Although the results presented in this paper have been obtained with an integrated JFET technology, the conclusions are valid for whatever technology the SF is made.