(A) study on CMOS time delay and integration readout circuit using capacitance control and charge transfer methods

Abstract

In this study, the readout circuits for a time delay and integration (TDI) array were discussed. Firstly, the readout circuit which improves signal-to-noise ratio (SNR) at low temperature is proposed for a satellite application. Next, a charge transfer readout circuit for an X-ray detector is proposed. Because some demerits of the TDI scheme can be solved by the proposed circuits, it is expected that the applications of the TDI scheme can be widen. The TDI array is adopted for a polar orbit satellite because a linear array instead of a staring array is used and the TDI scheme increases the SNR of the linear array. IR images acquired from the polar orbit satellites can be used in night-vision and weather forecasting. The IR radiation cannot penetrate a cloud, thus the cloud top temperature can be obtained by the IR images captured by the polar orbit satellites. Although the cloud top temperature is important in forecasting weather, it varies widely depending on the altitude of the cloud. Thus, a novel readout circuit which shows good performance over wide input range is required for environmental satellites. This dissertation proposes a novel CMOS readout circuit for satellite IR TDI arrays. In the proposed circuit, an adaptive charge capacity control method is used to improve the SNR at low temperature. Typical readout circuits show poor performance at low temperature target because the readout noise instead of the shot noise which is dominant at room temperature is dominant at low temperature. To solve the problem, the proposed circuit has a radiation prediction circuit which classifies the incident radiation into three regions. The circuit allocates proper capacitor proportional to the incident radiation. Thus, the readout noise can be reduced by the reduced capacitor size. The readout circuit was fabricated with a 0.35 μm CMOS process. By using the circuit, the SNR is increased as large as 15dB at 200K and 10dB at 220K. In addition, a simple dead pixel el...