  We have developed a new capacitive transimpedance amplifier (CTIA) that can
be operated at 2 K, and have good performance as readout circuits of
astronomical far-infrared array detectors. The circuit design of the present
CTIA consists of silicon p-MOSFETs and other passive elements. The process is a
standard Bi-CMOS process with 0.5$mu$m design rule. The open-loop gain of the
CTIA is more than 300, resulting in good integration performance. The output
voltage swing of the CTIA was 270 mV. The power consumption for each CTIA is
less than 10$mu$W. The noise at the output showed a$1/rm f$noise spectrum of
4$mu$V/$surdhbox Hz$at 1 Hz. The performance of this CTIA nearly fulfills the
requirements for the far-infrared array detectors onboard ASTRO-F, Japanese
infrared astronomical satellite to be launched in 2005.
