Readout Circuit Structure and Its Working Sequence Control Method

Abstract

The present invention provides a readout circuit structure and its working sequence control method. The readout circuit structure includes: a programmable gain amplifier circuit and an analog-to-digital converter circuit arranged in phase coupling, and the programmable gain amplifier circuit Comprising a sampling capacitor, a feedback capacitor, an operational amplifier and a reset control switch, the analog-to-digital converter circuit includes a comparator and a counter; wherein, one end of the reset control switch is connected to an input terminal of the operational amplifier, and the reset control The other end of the switch is connected to the output end of the comparator, the output end of the operational amplifier is connected to one input end of the comparator, and the other input end of the comparator is connected to a reference voltage. The technical scheme of the present invention enables the readout circuit structure to have the function of offset elimination and at the same time reduce the use of capacitors and switches to save area and power consumption, reduce the timing complexity of control signals and improve the overall circuit accuracy.

Description

technical field [0001] The present invention relates to the technical field of integrated circuits, in particular to a readout circuit structure and a method for controlling its working sequence. Background technique [0002] In CIS (CMOS Image Sensor, CMOS image sensor), it is usually necessary to convert the optical signal into a voltage signal in the photosensitive unit (pixel), then connect the PGA (Programmable Gain Amplifier, programmable gain amplifier) ​​to amplify the voltage signal, and then connect the ADC (Analog Digital Converter (analog-to-digital converter) circuit converts the analog voltage signal into a digital signal, and finally transmits the converted digital signal to the outside of the chip. Since the photosensitive units are usually in the form of an array, in order to improve the frame rate, each column of photosensitive units is usually connected to a column of readout circuits composed of PGA and ADC. [0003] see figure 1 , figure 1 is the sche...

AI Technical Summary

Problems solved by technology

Although this structure can achieve offset elimination and improve circuit accuracy, it needs to add at least 5 switches and 2 capacitors, such as image 3 The five switches of PGA_OS1, PGA_OS2, OS_C1, OS_C1N, and OS_C2 and the two capacitors of Cc and Cc2

Therefore, there are the following three problems in this structure: (1) Since the realization of the capacitor in the CMOS process occupies a relatively large area, increasing the two capacitors Cc and Cc2 will inevitably lead to a large total area to be occupied; (2) ) When the ADC performs analog-to-digital conversion, the parasitic capacitance Cp at the input terminal of the comparator COMP will form a capacitive voltage divider structure with the offset storage capacitor Cc2, so that the actual analog signal input of the ADC will be multiplied by Cc2 / (Cc2+Cp) this coefficient, which is obviously less than 1, that is, the actual analog signal input of the ADC is lost; (3) due to the increased number of switches, the control signal also increases correspondingly, which will cause the timing control of the readout circuit to be more complicated. like Figure 4 as shown, Figure 4 Yes image 3 The schematic diagram of the working timing of the readout circuit structure with the offset cancellation function shown, the entire circuit working timing cycle of the readout circuit structure can include the offset cancellation working phase and the normal programmable gain amplifier circuit and analog-to-digital converter circuit working phase (that is, the normal PGA+ADC working phase) these two phases

[0007] Therefore, it is necessary to propose a new readout circuit structure, so that the readout circuit structure can reduce the use of capacitors and switches while having the function of offset elimination, so as to save area and power consumption, reduce the timing complexity of control signals, and avoid Accuracy loss of existing structures to improve accuracy

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