A controllable piecewise linear-output circuit for CCD multiplexers

In certain applications, the single gain of the familiar reset-gate floating-diffusion output circuit limits the performance of a charge-coupled device (CCD) multiplexer used in a focal-plane array (FPA). Incorporation of an additional capacitor at the floating-diffusion node along with a switching MOSFET allows the output circuit to controllably switch from a high-gain to a low-gain state, thereby increasing the performance when detecting both large and small charge packets. This paper first describes such a circuit and then presents experimental results to verify its theory of operation. Discussion of a particular application is also given.