An 200 Msps 8-bit A/D converter with a duplex gray coding

This paper will report on a monolithic 8-bit parallel A/D converter which can digitize more than 50MHz input signal at 200 Msps without an external sample and hold circuit. Main remarkable feature are described as follows. (1) A dynamic circuit which latches data by using parasitic capacitances of the encoder is provided. (2) A new coding method which encodes a pair of outputs from comparators into a Gray code is adopted, so that the maximum error is suppressed within 4LSB, even if either of the output signals is missed. (3) High accuracy walled base and high speed walled emitter transistors with trench isolation are formed at the same time in order to realize high accuracy and high speed conversion. By using double ion implantation method, the distribution of offset voltages of the walled base transistor pairs is about 0.2mV as the standard deviation; 3 sigma. The walled base transistor is applied to only pre-amplifier stage of the comparator and the walled emitter transistor is applied to other digital circuits.