JPS5694833A - A/d converter - Google Patents

Abstract

PURPOSE:To realize not only a high speed but a high accuracy for an A/D converter, by combining the main and secondary clock pulses. CONSTITUTION:The main clock pulse given from the main clock generator 4 and having the repetitive frequency fM is applied to the wave crest-time converting circuit 1 to give a synchronous control to the rise of the square wave of the conversion output. Thus the units of the main clock pulses are counted in the form of the rough value of the time duration. On the other hand, the secondary clock generator 5 produces the clock pulse having a relation of [N/(N-1)].fM to the frequency fM to the frequency fM of the main clock pulse. The generator 5 is driven to start the generation of the secondary clock pulse synchronizing with the end of the square wave signal of the circuit 1, i.e., synchronizing with the discontinuation of counting of the main counter 3. The secondary clock pulse is compared with the main clockpulse through the phase comparator 6, the the secondary clock pulses are counted until a coincidence is obtained in the above comparison. As a result, a counting is possible with an accuracy of N times as high as that of only main clock pulse.