Patent ID: 6819281
Filing Date: 2004-11-16
Classification: H03M,H04N

Abstract:
An A/D conversion circuit, which converts an analog value input at the input end into a digital value and outputs the digital value at the output end, comprising:an amplifier having a first input terminal, second input terminal, and output terminal, said first input terminal of which is connected to said input end via a coupling capacitor, and to said second input terminal of which is input a common voltage Vcom; a feedback capacitor, provided between said first input terminal and said output terminal of said amplifier; a switch, provided between said first input terminal and said output terminal of said amplifier; a number M of variable capacitance portions, each having a number Nm of capacitance elements one end of each of which is connected to said first input terminal of said amplifier and having different capacitance values, and voltage switching means which switches a voltage for input to the other end of the respective said Nm capacitors, between said common voltage Vcom and any of a number Pm of reference voltages Vrgf,m,1 to Vref,m,Pm, wherein M&gE;1, Nm&gE;1, Pm&gE;1, 1&lE;m&lE;M, but excluding the case M=P1=1; a comparison portion, which compares the magnitudes of the voltage output from said output terminal of said amplifier and said common voltage Vcom, and outputs a signal indicating the comparison result; and, a capacitance control portion, which controls the switching operations of each of said voltage switching means of said M variable capacitance portions, and which outputs to said output end a digital value based on the switched states of each of said voltage switching means of said M variable capacitance portions as well as on the signal output from said comparison portion.