An 8b 150 MSample/s serial ADC

An 8 b bipolar ADC demonstrates a serial-ripple architecture that has several advantages over a traditional flash architecture. The typical 8 b flash ADC has 255 comparators which results in high input capacitance, large die size, and high power dissipation. The converter described here achieves a 150 MSample/s conversion rate with only 12 comparators and 350 mW power dissipation. At the input to the converter is a master/slave (M/S) track-and-hold amplifier (T/H), used to give the serial converter a full clock period to settle. The converter consists of five serially-connected folding amplifiers (called magnitude amplifiers, or magamps) and one 3 b flash. Each magamp accepts a differential analog input, resolves one bit of data using an internal comparator, and produces a folded differential analog output signal for the next stage. The converter is fabricated in a 1 /spl mu/m 8 GHz BiCMOS process. This prototype uses only 780 bipolar transistors and dissipates 350 mW from a single 5 V supply. Power dissipation is essentially independent of encode rate and input frequency.