An aid conversion technique which combines some of the speed advantages of flash conversion with the circuitry savings of successive approximation is termed half-flash. In an 8-bit, half-flash converter, two 4-bit flash aid sections are combined. The upper flash aid compares the input signal to the reference and generates the upper 4 data bits. This data goes to an internal DAC, whose output is subtracted from the analog input.
Then, the difference can be measured by the second flash aid, which provides the lower 4 data bits.