4.2K MULTICHANNEL READOUT CIRCUITRY IN A STANDARD 0.7µm PROCESS FOR A PHOTOCONDUCTOR ARRAY

With the increasing performance of infrared sensors (i.e. dark current, QE, noise), the performance of the analog read-out electronics becomes more and more a determining factor in the overall system performance. For low temperature readout circuits, dedicated architectures and design techniques are needed rather than a translation of uncooled circuitry by trial and error. In this paper we present the cryogenic design and performance of a cold CMOS multichannel readout circuit to be used for the Ge:Ga focal plane detectors in the Photoconductor Array Camera and Spectrometer (PACS) aboard the Herschel Space Observatory. Key issues in the design of this 18-channel readout are noise, bias stability, linearity and low power consumption. As the specifications in this project are tighter than in our previous cryogenic designs for ISOPHOT, the use of robust architectures and design techniques is essential. Both simulations and cryogenic tests show an amplifier open loop gain above 2000, a non-linearity error below 2 % over a dynamic output range of more than 2 V and an input-referred noise spectral density of less than 200 nV / Hz at 30 Hz for a total power consumption of 100 µW for the 18 channels