Readout Circuit For Integrated Sensor

Uncooled infrared image sensors have a wide range of applications. In manymaterials, SOI diode detectors have good sensitivity and consistency. A digitalreadout circuit (ROIC) for such detector is designed in this paper. The scale of thedetector array is160×120, the pixel pitch is32μm and the frame rate is100Hz.Considering the uncooled infrared detector array with a large array and small pixelpitch, the system uses a column-wise architecture through the trade-offs betweenpower and area. The integrating ADC structure as a scalable ROIC and the first-orderincremental Sigma-Delta ADC structure as a low-noise, low power readout ROIC areanalyzed and designed.In the scalable ROIC structure, the relative offset between column cells isreduced by subtracting it with an additional reference column; the background signalis eliminated through a differential input of Gm-C integrator; the output range of thecolumn cells is calibrated by the use of another integrator with tunable input as theslope generation unit. Appling0.35μm CMOS process, eight columns of readoutcircuit are designed and tested. The results of the test show that, the maximum inputequivalent offset between column cells is only3mV. However the noise and linearityis poor.As the second ROIC structure，the first-order Incremental Sigma-Delta ADCstructure has good linearity. Through applying chopper in the circuit, the flicker noisecan be suppressed. Typical integrator is replaced by a bilinear integrator, thus thefrequency of system clock is halved. For the sake of no slew rate limitation in theclass AB OTA, the power dissipation is reduced by the low tail current biasing. Thisstructure of ROIC is designed in0.18μm CMOS process and simulations areperformed to verify its low noise and low power performance.