PULSE WIDTH MODULATING CIRCUIT

PURPOSE:To simplify the circuit and to improve the performance, by using one switching element, and flowing a current from a reference voltage circuit steadily to an amplifier. CONSTITUTION:A DC signal E1 to be measured is applied to an input terminal 1. An integrator consisting of a capacitor C and an amplifier U1 sums and integrates a current ip from a reference voltage Ep, a current E1/R1 from the DC signal E1, and a current iN from a reference voltage EN. Further, a switching element S1 is controlled so that the algebraic sum of three currents flowing to the integrator is zero at one period of integration. Formula as shown is obtained, where T is the time of one period of integration, T1 is a time when the S1 is turned on at the T, and T2 is the residual time. Thus, the DC signal E1 to be measured can be obtained by counting the T1 and T. By adopting the automatic zero system, the remaining zero can automatically be corrected, giving no effect on the measuring accuracy.