The invention provides an A/D converter which comprises reference voltage generator means for generating a plurality of reference input voltages from a power supply, a comparator composed of switching means for inputting into the A/D converter an external analog input voltage and the reference input voltages and of an amplifier for amplifying the respective input voltages, and control means for controlling the reference voltage generator means and the comparator on the basis of an output from the comparator; the amplifier circuit of the comparator sharing its power supply with the reference voltage generator means.

A digital to analog converter is disclosed which can operate with a high accuracy and can be fabricated at a highly integrated structure. The converter comprises a voltage divider circuit dividing a reference voltage into a plurality of divided voltages, a plurality of P-channel field effect transistor switches for selectively extracting a higher potential part of the divided voltages and a plurality of N-channel field effect transistor switches for selectively extracting a lower potential part of the divided voltages, wherein both of P-channel and N-channel transistors operate in a triode-region.

An apparatus for converting the sum of m digital signals to an analog signal utilizing resistors and switches only. The operating time of the apparatus is the time required to pass the signal through a single switch. This invention can also be utilized in an A/D converter for converting the difference between an analog signal and several digital signals to a digital signal without using extra time to compute the subtraction.

The A-D converter of the present invention is a sequential comparing A-D converter having a chopper stable comparator built therein and comprises: using on/off switches each in the form of an NMOS FET, a third on/off switch interposed between a first input terminal of a differential amplifier and a grounding terminal for opening or closing the connection between the terminals, a fourth on/off switch interposed between a second input terminal of the differential amplifier and the grounding terminal for opening or closing the connection between the terminals, a fifth on/off switch interposed between the first and second input terminals of the differential amplifier for opening or closing the connection between the terminals, and a NOR circuit for inputting a boosting signal .phi. from the front and the rear of an inverter, and a condenser whose one terminal is grounded and which outputs a driving pulse to the gates of the three third, fourth and fifth on/off switches.

A D/A converter is comprised of a string of resistors coupled to a voltage source with respective junctions formed between adjacent resistors, including a reference junction substantially at the mid-point of the resistor string. Plural switches are coupled to the junctions and are selectively operable to couple a potential produced at a respective junction. A subtracting circuit has one input coupled in common to a first set of the switches and another input coupled in common to a second set of the switches to subtract the potential coupled from one set from the potential coupled from the other set so as to produce an output analog signal. A switch control circuit is responsive to a multi-bit digital signal for operating predetermined switches in both the first and second sets and thereby couple to the subtracting circuit the potentials which are produced at corresponding junctions on either side of the reference junction.