1. W. Kester, Editor, Amplifier Applications Guide, Analog Devices, 1992, ISBN-0-916550-10-9, Chapter 10. (An excellent discussion by James Bryant on the use of op amps as comparators.)
2. J.N. Giles, “High Speed Transistor Difference Amplifier,” US Patent 3,843,934, filed, January 31, 1973, issued October 22, 1974. (Describes one of the first high-speed ECL comparators, the AM685.)
3. A 400-MHz Input Flash Converter with Error Correction;Mangelsdorf;IEEE Journal of Solid-State Circuits,1990
4. A Monolithic Voltage-Comparator Array for A/D Converters;Woodward;IEEE Journal of Solid State Circuits,1975
5. P.M. Rainey, “Facsimile Telegraph System,” US Patent 1,608,527, filed, July 20, 1921, issued November 30, 1926. (Although A.H. Reeves is generally credited with the invention of PCM, this patent discloses an electro-mechanical PCM system complete with A/D and D/A converters. The 5-bit electro-mechanical ADC described is probably the first documented flash converter. The patent was largely ignored and forgotten until many years after the various Reeves' patents were issued in 1939–1942.)