Analogue Digital Converter and Method for converting Analogue to Digital in CMOS image Sensor

摘要

An ADC(Analog to Digital Converter) of a CMOS(Complementary Metal Oxide Semiconductor) image sensor and an analog to digital conversion method are provided to perform ADC operation with high precision in a small area by performing a function of a lamp generator by using a capacitor array, arranged per column of a pixel array, for storing a reset voltage and a pixel signal voltage without composing the additional lamp generator. A plurality of comparison circuits(4121-412N) compares a pixel signal with a reset signal, respectively. A column direction memory block(54) stores a gray code in response to a corresponding output signal among output signals of a plurality of the comparison circuits(4121-412N). Each of a plurality of the comparison circuits(4121-412N) includes a switch block having switches(SW11,SW21,SW31,SW41,SW51,SW61), a comparator(COM1), and a capacitor array. The switch block supplies one of the first to the third reference voltages to one corresponding node among the first to the fourth nodes. The comparator(COM1) has the first input terminal for receiving the pixel signal and the second input terminal for receiving the reset signal. The capacitor array includes the first to the fourth capacitors(C11,C21,C31,C41). The first capacitor(C11) is connected between the third node and the first node. The second capacitor(C21) is connected between the fourth node and the second node. The third capacitor(C31) is connected between the first node and the first input terminal. The fourth capacitor(C41) is connected between the second node and the second input terminal.