JPS554116A - Analog-to-digital converter - Google Patents

Abstract

PURPOSE: To obtain a high-precision analog-to-digital converter with its conversion time much shorter than that of a conventional integral system, by providing two factors, the integral system and parallel comparison system which is one of non- feedback systems.

CONSTITUTION: An input signal current from input terminal 1 and a reference current from reference current supply 6 are both led to the input terminal of integrator 3. Both currents are different in polarity. The output of integrator 3 is supplied to one-side terminals of voltage comparators 8 to 11 while voltages whose values are set in the order of V₁, V₂, V₃, and V₄ from smallest to largest are applied to other-side terminals. The outputs of voltage comparators 8 to 11 are led to digital control circuit 12, where a decision on the output state of comparator 11 is made on every arrival of the clock signal of clock pulse generating circuit 13, so that charge accumulated in integral capacitor 4 will be balanced under the control of the input signal current and reference current. Then, the number of times of supplying the reference current during analog-to-digital conversion is set to upper bits of output data and the amount of remaining charge in capacitor 4 right after the end of the conversion is decided on, so that a decision on lower bits of the output data will be made according to the amount of the remaining charge.

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