A/D converter with noise cancel function

An A/D converter with a function of noise cancellation of a signal including first and second voltage levels alternately arranged, the first voltage level containing a noise component, the second voltage level containing a significant signal component and a noise component, the significant signal component being superimposed on the noise component, the function of noise cancellation being provided by subtracting the first voltage level from the second voltage level, the A/D converter comprising:

• amplifying means (1) for amplifying an input signal;
• a first capacitor (C1) for storing a voltage level, the voltage level being generated at an output of the amplifying means from the first voltage level;
• a second capacitor (C2) for storing a voltage level, the voltage level being generated at the output of the amplifying means from the second voltage level;
• a comparator (2, 3) coupled to the output of the amplifying means;
• a D/A converter (5) controlled by a comparison result of the comparator;
• switching means for switching connection of the first and second capacitors to between an input of the amplifying means (1) and the D/A conversion section (5);
• and
• a control section for controlling turning-on and turning-off of the switching means, the switching means changing the connection of the first and second capacitors to between the input of the amplifying means (1) and the D/A converter (5) to produce a difference between a voltage of the first capacitor and a voltage of the second capacitor at the output of the amplifying means and to perform cyclic A/D conversion of the difference using the first and second capacitors.