A/D converter that is implemented using only digital circuit components and digital signal processing

An A/D (analog-to-digital) converter for repetitively converting a level of a converter input voltage to an output digital numeric value in successive measurement intervals, said A/D converter comprising:

• a pulse delay circuit comprising a plurality of delay units connected as successive delay stages, with a first-stage one of said delay units receiving an externally supplied pulse signal at commencement of each of said measurement intervals, with said converter input voltage being applied to control each of said delay units, and each of said delay units transferring said pulse signal with an amount of delay that varies in accordance with said level of the converter input voltage, and
• encoder circuit means coupled to receive respective outputs of said delay units, for detecting a total number of said delay stages that have been traversed by said pulse signal up to the end of said measurement interval and for deriving from said total number at least a set of low-order bits of said output digital value,
• each of said pulse delay circuit and said encoder circuit means comprising a plurality of transistors;
• wherein at each of respective values of said converter input voltage level, said delay units uniformly produce a corresponding predetermined amount of delay, and
• each of the transistors of said pulse delay circuit is formed with a larger size than transistors constituting specific other sections of the A/D converter, said specific other sections including at least a part of said encoder circuit means.