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In order to make medium-long wave HgCdTe IR detector work normally it
must be in zero bias voltage, the differential input current preamplifier can easily make
HgCdTe IR detector biased at zero voltage. Because IR signals are often very weak, then little
disturb can affect the performance of the total detector system very much. In order to achieve
high Signal-to-Noise ratio, it is expected that the differential input current preamplifier can be
designed to work as close as to the HgCdTe IR detector. That is to say the preamplifier can
also work normally at 77K. In this paper, a high-performance low-noise differential input
current preamplifier working at cryogenic temperature for HgCdTe IR detectors is designed.
Since a differential input folded-cascode structure has been used in the preamplifier's design,
it makes that the gain of single stage amplifier can arrive 60dB, the circuit uses high resistant
poly as feedback resistance so that 40 MΩ feedback resistance can be integrated on chip at
temperature 77k ,which can directly transforms IR detector's current to voltage, avoiding the
additional noise by using exterior resister. The preamplifier's noise characteristics were
analyzed and the methods for decreasing noise were proposed. This differential input current
preamplifier was implemented in 0.5μm CMOS process. The size of eight-cell chip is
3mm×1.9mm. The test result shows that the current preamplifier has good performance at the
temperature of 77K. Within the bandwidth of 3.3KHz, the total output voltage noise is 120uV,
the equivalent total input noise voltage is 3PA, the equivalent input noise current is
0.03pA/Hz1/2@100Hz. The preamplifier power consumption is less than 1mW at 77K. When
the input current is less than 10nA, its linearity has been reached 99%. This circuit can work
normally at temperature between 300K to 77K and it can be used for several bands of IR
detector. Finally, it can work normally either by ±2 or by ±1.5 voltage power supply. This current preamplifier has been successfully applied in the signal readout of HgCdTe IR
detectors for infrared imaging.
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