A novel CMOS snapshot readout structure called DCA (Direct-injection Charge Amplifier) for focal-plane array (FPA) is presented in this paper.The pixel circuit includes only four MOS transistors.Using PMOSFET as the reset transistor with careful layout design

this pixel circuit not only can keep the in-pixel-capacitance large enough

but also can avoid the threshold voltage loss during the reset for the integration node.Thereby

charge capacity of the readout circuit is increased.Since the pixel circuit is very simple and this structure can eliminate the influence of column bus parasitic capacitance

it is very suitable for large-format small-pixel readout circuit.An experimental 12

8×128 DCA chip has been designed with 1.2-μm DPDM n-well CMOS technology.The charge handling capacity is 11.2pC with pixel size 50×50μm

2

.A description of the readout circuit structure

pixel circuit

detector model

operation principle and chip layout is given in detail.Both excellent simulation results and experimental results of the fabricated DCA readout chip are presented.