The most common type of A/D converter is the Successive Approximation Converter. This device actually contains a D/A, an analog comparator, and a state machine. Through a series of successive tests, the D/A walks through each bit, setting it to 1 and then checking if the resulting output value is less than or greater than the input signal. The result of the comparison dictates whether the bit stays a 1 or returns to 0. Then the circuit moves on to the next bit. After all bits have been tested in this manner, the resulting final value is the closest approximation to the input signal voltage. This final value is returned as the A/D conveter's digital value.