A/D converter

An A/D converter, comprising:

• a capacitor type D/A conversion circuit for outputting a first comparison potential correspondingly to a value of high-order L bit (L is an integer) of inputted comparison digital data;
• a plurality of resistor type D/A conversion circuits for outputting potentials obtained by dividing supplied power supply voltage in combination, respectively, correspondingly to a value of low-order M bit (M is an integer) of the comparison digital data;
• a plurality of coupling capacitors provided correspondingly to said plurality of resistor type D/A conversion circuits, each of one ends of the plurality of coupling capacitors being connected to a corresponding output terminal of said resistor type D/A conversion circuit, and the other ends being commonly connected to an output terminal of said capacitor type D/A conversion circuit;
• a comparing circuit for comparing a sum of a second comparison potential obtained by weighting and adding the output potentials of said plurality of resistor type D/A conversion circuits based on capacitance values of said corresponding coupling capacitors, and the first comparison potential, with a potential of an input analog signal inputted from the outside;
• and
• a control circuit for deciding a value of output digital data corresponding to the potential of the input analog signal by each bit and generating new comparison digital data, based on the comparison result by said comparing circuit, repeatedly performing control of said capacitor type D/A conversion circuit and said plurality of resistor type D/A conversion circuits based on sequentially generated comparison digital data, and converting the input analog signal into an output digital signal of (L+M) bits and outputting the output digital signal,
• wherein said control circuit controls said plurality of resistor type D/A conversion circuits so that a potential corresponding to the value of the low-order M bit of the comparison digital data out of potentials obtained by dividing the power supply voltage into 2M and the second comparison potential become equal to each other.

An A/D converter, comprising:

• a capacitor type D/A conversion circuit for outputting a first comparison potential correspondingly to a value of high-order L bit (L is an integer) of inputted comparison digital data;
• a resistor type D/A conversion circuit for outputting a second comparison potential correspondingly to a value of low-order M bit (M is an integer) of the comparison digital data;
• a coupling capacitor one end of which being connected to an output terminal of said resistor type D/A conversion circuit and the other end of which being connected to an output terminal of said capacitor type D/A conversion circuit;
• a comparing circuit for comparing a sum of the first comparison potential and the second comparison potential, with a potential of an input analog signal inputted from the outside;
• a control circuit for deciding a value of output digital data corresponding to the potential of the input analog signal by each bit and generating new comparison digital data, based on the comparison result by said comparing circuit, repeatedly performing control of said capacitor type D/A conversion circuit and said resistor type D/A conversion circuit based on sequentially generated comparison digital data, and converting the input analog signal into an output digital signal of (L+M) bits and outputting the output digital signal;
• and
• an initial potential supply circuit for outputting a potential of ½ of a potential corresponding to the least significant bit of the comparison digital data to said coupling capacitor when the input analog signal is sampled.