JPS56168429A - Analog-to-digital converter - Google Patents

Abstract

PURPOSE:To ensure an A/D conversion of high accuracy, by converting the voltage to be converted into a digital quantity based on a ratio of time interval by which coincidence is obtained for the upper and lower limit reference voltages and the voltage to be converted with the triangular wave voltage. CONSTITUTION:A triagngular wave generating circuit 4 generates the triangular wave voltage. A comparator 5 compares the lower limit reference voltage V1 with the triangular wave output voltage and produces a coincidence signal when coincidence is obtained. Then a CPU6 starts a timing to change an input terminal from S3 to S1. When the triangular wave voltage increases up to coincide with the voltage Vx to be converted, a coincidence signal is produced from the comparator. Thus the timing is discontinued and the timing value is stored. Then a timing is newly started to switch the input terminal to S2. When coincidence is obtained between the upper limit reference voltage V2 and the triangular wave voltage, a coincidence signal is produced from the circuit 5. Then the CPU6 stops the timing to read the value of timing. The voltage Vx is calculated from these two timing values.