A successive approximation ADC is a type of analog-to-digital converter

Analog-to-digital converter

An analog-to-digital converter is a device that converts a continuous quantity to a discrete time digital representation. An ADC may also provide an isolated measurement...

 that converts a continuous analog

Analog signal

An analog or analogue signal is any continuous signal for which the time varying feature of the signal is a representation of some other time varying quantity, i.e., analogous to another time varying signal. It differs from a digital signal in terms of small fluctuations in the signal which are...

 waveform into a discrete digital

Digital

A digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...

 representation via a binary search through all possible quantization

Quantization (signal processing)

Quantization, in mathematics and digital signal processing, is the process of mapping a large set of input values to a smaller set – such as rounding values to some unit of precision. A device or algorithmic function that performs quantization is called a quantizer. The error introduced by...

 levels before finally converging upon a digital output for each conversion.
Key

• DAC = Digital-to-Analog converter
• EOC = end of conversion
• SAR = successive approximation register
• S/H = sample and hold circuit
• V_in = input voltage
• V_ref = reference voltage

The successive approximation Analog to digital converter circuit typically consists of four chief subcircuits:

1. A sample and hold circuit to acquire the input voltage
   Voltage
   Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
   
    (V_in).
2. An analog voltage comparator that compares V_in to the output of the internal DAC
   Digital-to-analog converter
   In electronics, a digital-to-analog converter is a device that converts a digital code to an analog signal . An analog-to-digital converter performs the reverse operation...
   
    and outputs the result of the comparison to the successive approximation register
   Processor register
   In computer architecture, a processor register is a small amount of storage available as part of a CPU or other digital processor. Such registers are addressed by mechanisms other than main memory and can be accessed more quickly...
   
    (SAR).
3. A successive approximation register subcircuit designed to supply an approximate digital code of V_in to the internal DAC.
4. An internal reference DAC that supplies the comparator
   Comparator
   In electronics, a comparator is a device that compares two voltages or currents and switches its output to indicate which is larger. They are commonly used in devices such as Analog-to-digital converters .- Input voltage range :...
   
    with an analog voltage equivalent of the digital code output of the SAR for comparison with V_in.

The successive approximation register is initialized so that the most significant bit

Most significant bit

In computing, the most significant bit is the bit position in a binary number having the greatest value...

 (MSB) is equal to a digital

Digital

A digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...

 1.