| Some bands in ultraviolet radiation have a near-zero "day-blind" background and a uniformly distributed "visible blind" scattering background,which makes ultraviolet detection(UV)technology have good development prospects in both military and civilian fields.UV detection system generally consists of UV optical system,UV focal plane array(FPA),readout circuit and subsequent signal processing circuit.Among them,the readout circuit is used to process the weak UV detection signal by the way of integral amplification,which is convenient for further processing of the follow-up system.As a very critical part of the UV detection system,the readout circuit will directly affect the performance of the entire UV detection system.Traditional readout circuits usually use line-by-line integration or sequential integration to process the photo-generated current.This circuit brings a lot of noise and poor image quality.At the same time,the photo-generated current output by the UV detector has a certain limit on the integration time of the readout circuit.Different photogenerated current has different requirements on the integration time.Therefore,how to design the readout circuit to be compatible with both the large photocurrent and small photocurrent has become a key research direction.Besides,when the photo-generated current output by the ultraviolet detector is very weak,the integration circuit will produce leakage current during its processing,which will affect the linearity of the integration result,resulting in inaccuracy of the output result.Therefore,reducing the leakage current and improving the linearity is a difficult point in the design of the readout circuit.Therefore,this dissertation adopts the method of pixel simultaneous integration to form a pixel-level readout circuit.This circuit can eliminate the disadvantages caused by the traditional readout circuit and improve the image quality to avoid the phenomenon of tailing.Simultaneously,two working modes are designed to satisfy the situation where the photo-generated current is large and the photo-generated current is small.One is the integral re-output mode,which is suitable for the case where the UV detector generates a large current;the other is the integration simultaneous output mode,which is suitable for the case where the UV detector generates a small current.In addition,for the problem of leakage current caused by the circuit when dealing with weak photo-generated current,this paper proposes an improved capacitive feedback transimpedance amplifier(CTIA)structure composed of CMOS differential amplifiers.At the same time,this paper also designs and simulates the sampling circuit,analog buffer output stage circuit and temperature sensor,and in order to ensure the normal operation of the readout circuit,this paper has designed a digital timing control circuit,including the integral reset and sampling required for the normal operation of the unit circuit and row select and column select signal.Based on SMIC 0.18 ?m CMOS process,this paper designed and simulated a pixellevel readout circuit of an ultraviolet focal plane detector with a frame frequency of 100 Hz,a maximum transmission rate of 20 MHz,and an array of 640 × 512.According to the simulation results,the improved CTIA structure can effectively reduce the leakage current.When the input current is 300 fA,the leakage current is reduced to 1/4 of the original structure.The structure improves the linearity to 99.9%,and the power consumption is only 57.6 nW;analog buffer output stage circuit used unity gain amplifier,in which the open loop gain of the op amp is 78.39 dB,unity gain bandwidth is 46.53 MHz,and the input range is 0-2.885 V. |
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