In our study, we designed a 512×512 readout integrated circuit (ROIC) for N-on-P short wave infrared
(SWIR) detectors, which has the ability to operate with two capacitors for different input current levels
from very low background applications to daytime high illumination conditions. A buffered direct
injection (BDI) readout cell as input circuit provides a low input resistance, high injection efficiency,
and precise biasing voltage to the photodiode at low input currents. In order to reduce the noise of the
BDI readout cell, a high-performance single stage amplifier is devised, the gain of which reaches as
high as 50dB. The input MOSFET of the amplifier operates at sub-threshold region to keep the
photodiode at precise reverse bias and steady injection efficiency. At the same time, with the input
MOSFET at sub-threshold region, the current is smaller than at saturation region, and the power
dissipation is reduced to a low level. A sample and hold circuit is also part of the input unit cell
architecture, which allows the infrared focal plane array (IRFPA) to be operated in full frame snapshot
mode and rolling mode. To prevent the excess of total current of the ROIC, the reset time of every row
has a lag of one period compared to the previous row. The simulation results confirm these advantages.
With the 5.0V power supply, ROIC provides the output dynamic range over 2.5V, the well capacity
more than 1×106e-, and the total power dissipation less than 120mW. The final chip is fabricated with
HHNEC 0.35um 1P4M process technology, and the pixel occupies a 30um×30um area. The Testing
results are coincide with the simulations of the circuit. With the detecting current varies from 30pA to
1nA, the linearity of BDI is 99%, and it can be operated at the temperatures below 77K.
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