Research On Analog Over-Sampled Image Restoration Circuit For TDI CMOS Image Sensor

Time-Delay-Integration(TDI)image sensor can get higher signal-to-noise ratio under the condition of dark light environment and high scanning speed,so,it is widely used in the fields of space imaging,aerial photography,industrial scanning and medical imaging.However,in order to ensure the image quality of a single acquisition,the pixel size of TDI CMOS image sensors is often larger than that of traditional image sensors.Therefore,the study of TDI CMOS image sensors with high resolution has become one of the research hotspots.Existing technologies to improve the resolution of TDI CMOS image sensors mainly include linear interpolation(parity pixel array)technology and over-sampling technology,among which the over-sampling technology does not need to modify the pixel array,so it has higher process compatibility.The images obtained by oversampling will overlap in the direction of sensor motion,which will make the images blurred and need to be restored.The integration degree of digital over-sampled image restoration system is low,so it is very important to study the analog over-sampled image restoration circuit.In this paper,the working principle of the over-sampled image restoration of TDI CMOS image sensor is analyzed.According to the characteristics of the over-sampled image restoration algorithm,the scheme of over-sampled image restoration in the analog domain is proposed.Secondly,an analog over-sampled image restoration circuit with 16-level high precision four-quadrant analog multiplication and accumulation(MAC)circuit as the core is designed.In order to meet the high precision requirements of multiplication and accumulation operation,the analog MAC uses programmable sampling capacitor array instead of the sampling capacitor of the traditional analog accumulator to realize multiplication and accumulation operation,avoiding the problem of poor accuracy with open-loop multiplier.At the same time,the analog multiplier and the analog accumulator are combined to share a fully differential operational amplifier to reduce the chip area and power consumption,and reduce the complexity of timing control.According to the requirement of four quadrants of multiplication and accumulation operation,the digital sequential control is adopted to control the sequence in which the differential output signals of the sampling circuit are connected to the MAC.Then,a two-step SS ADC was designed to quantify the restored image,to solve the problem of process deviation,an integral self-calibration ramp generator is designed.By dynamically adjusting the gate voltage of the integrating current source,the integral current is adjusted to obtain the exact slope slope.In order to solve the problem of fixed pattern noise caused by offset voltage in the column level comparator,a three-stage pre-amplification and dynamic latch structure is adopted.The pre-amplification circuit is used to suppress the offset voltage of the dynamic latch,and its own offset voltage is eliminated by output offset storage technology,which greatly reduces the fixed pattern noise.In this paper,based on the UMC 110nm CMOS process,analog over-sampled image restoration circuit and column-level two-step SS ADC of TDI CMOS image sensor are designed.The single column area of the analog over-sampled image restoration circuit is 3072μm×40μm.The postsimulation results show that under the condition of 3 906 lines/s,it can restore the over-sampled image of the 4-stage TDI CMOS image sensor at 2 times sampling frequency.Compared with the traditional single linear array imaging method,the image resolution is doubled in the direction of sensor motion,and the SNR is increased by 8.71 dB.The single column area of the column-level two-step SS ADC is 331μm×40μm.Under the sampling frequency of 210.526KSps and input sinusoidal signal of 20.7648KHZ,the post-simulation results of dynamic characteristics show that:SFDR is 76.5dB,THD is-66.4dB,SNR is 59.5dB,SNDR is 58.7dB,ENOB is 9.44-bit.The post-simulation results of static characteristics DNL is-0.5/+0.5LSB,INL is-0.3/+0.6LSB.