Noise performance of pixel readout electronics using very small area devices in CMOS technology

The readout electronics for radiation pixel detectors must have low-power dissipation and small die area. Under these constraints, it is possible that the standard design approach will lead to strongly underestimated noise values, when small area devices are used. This work proposes a set of equations for a better approximation of the ENC of the front-end amplifier. All the possible noise sources are taken into account, including the transistor that realizes the feedback resistor of the charge amplifier. Furthermore, minimum noise conditions are proposed with respect to the width of input transistor and the shaping time. Several readout chains have been designed and measured, in a 0.8 μm CMOS technology. A specific one, designed by the proposed methodology in order to match a pixel detector of 15 fF capacitance, exhibits 15.3 e− rms ENC and 380 mV/fC gain with shaping time of 160 ns and power dissipation of 215 μW.