Design of ROIC based on switched capacitor TDI for MCT LWIR focal plane arrays


Design and measurement of a silicon readout integrated circuit (ROIC) based on switched capacitor time delay integration (TDI) technique for LWIR HgCdTe Focal Plane is presented. ROIC incorporates time delay integration (TDI) functionality for scanning type of detector by using switched capacitor technique with a supersampling rate of three, increasing SNR and the spatial resolution. ROIC, in terms of functionality, is capable of bidirectional scan, programmable integration time, 5 gain settings at the input and auto gain adjustment with pixel deselection capability. Programming can be done parallel or serially with test mode functionality. ROIC can handle up to 3.75V dynamic range with the load being 25pF capacitive, output settling time is less than 80 nsec. This low power ROIC consumes less than 100mW. Moreover, input referred noise is less than 750 rms electrons. Simulations and measurements are done in both room temperature and cryogenic (77 °K) temperatures. In order to measure and simulate chip without a detector, process and temperature invariant current source block that imitate detector currents are designed as well. The manufacturing technology is 0.35μm, double poly-Si, four-metal (3 metals and 1 top metal) 5V CMOS process.