Analog-digital converter

An analog-digital converter comprising first and second signal input terminals to which is selectively applied through an analog switch means any one of an input analog voltage, a first reference voltage and a second reference voltage;

• an integration circuit having first and second integration resistors selectively connected to said first and second signal input terminals, a D.C. amplifier having an inversion input terminal to which said first and second integration resistors are connected and a non-inversion input terminal to which is applied a specified voltage having an intermediate value between said first and second reference voltages, and an integration capacitor connected between an output terminal of said D.C. amplifier and said inverstion input terminal;
• an analog comparator having a first input terminal connected to said output terminal of said D.C. amplifier and a second input terminal to which is applied a comparing reference voltage;
• and a control circuit for selectively applying through said analog switch means any one of said analog voltage, said first reference voltage and said second reference voltage to said first and second signal input terminals upon receipt of an output signal of said analog comparator, characterized in that said control circuit comprises a counter for counting clock pulses for a specified length of time T.sub.1 from the point of time when said analog comparator has detected that the output voltage of said D.C. amplifier has coincided with said comparing reference voltage, to produce an output signal while said first reference voltage is applied to said first and second signal input terminals, a changing-over means for changing over a voltage being applied to said first and second signal input terminals to said second reference voltage at the point of time when said counter has counted clock pulses for said specified length of time T.sub.1, a first measuring means for measuring a length of time T.sub.2 from the point of time when said voltage being applied has been changed over to said second reference voltage by said changing-over means to the point of time when said analog comparator again produces an output signal, a first determining means for determining from said time length T.sub.2 measured by said first measuring means and said specified time length T.sub.1 an error in terms of time length due to the offset voltage of said integtation circuit, a second determining means for determining a specified length of Time T.sub.3 necessary to measure said input voltage using said time length errors determined by said first determining means, a first applying means for applying said input voltage to said first signal output terminal for an initial substantial half period T.sub.3 /2 of said specified time length T.sub.3 determined by said second determining means and simultaneously applying said first or second reference voltage to said second signal input terminal and thereafter applying said reference voltages applied during said initial substantial half period T.sub.3 /2 to said first signal input terminal for the remaining substantial half period T.sub.3 /2 and simultaneously applying said input voltage to said second signal input terminal, a second applying means for applying, after said prescribed voltages have been applied by said first applying means to said first and second signal input terminals, said first or second reference voltage to said first and second signal input terminals, a second measuring means for measuring a length of time T.sub.4 from the point of time when a voltage being applied by said second applying means has been changed over to the point of time when said analog comparator again produces an output signal, and a second determining means for determining a digital amount of said input voltage from said time length T.sub.4 measured by said second measuring means and said specified time length T.sub.1.

An analog-digital converter comprising first and second signal input terminals to which is selectively applied through an analog switch means any one of an input analog voltage, a first reference voltage and a second reference voltage;

• an integration circuit having first and second integration resistors selectively connected to said first and second signal input terminals, a D.C. amplifier having an inversion input terminal to which said first and second integration resistors are connected and a non-inversion input terminal to which is applied a specified voltage having an intermediate value between said first and second reference voltages, and an integration capacitor connected between an output terminal of said D.C. amplifier and said inversion input terminal;
• an analog comparator having a first input terminal connected to said output terminal of said D.C. amplifier and a second input terminal to which is applied a comparing reference voltage;
• and a control circuit for selectively applying through said analog switch means any one of said analog voltage, said first reference voltage and said second reference voltage to said first and second signal input terminals, characterized in that said control circuit comprises a first changing-over means for changing over said analog switch means so as to apply said input voltage and either one of said first and second reference voltages to said first and second integration resistors, a second changing-over means for changing over said analog switch means so as to apply one of said first and second reference voltages to said first and second integration resistors commonly, a third changing-over means for changing over said analog switch means so as to apply said input voltage and either one of said first and second reference voltages which is same as said first changing-over means to said first and second integration resistors respectively in a manner combined differently from said first changing-over means, and means for obtaining a digital value corresponding to a sum of output voltages of said integrator obtained by said first, second and third changing-over means, whereby an A-D converted amount of said input voltage is obtained using said digital value obtained by said last means.