12b 50MSample/s two-stage A/D converter

A 12 b 50 MSample/s two-stage A/D converter in a complementary bipolar process uses coarse and fine encoders based upon a cascaded magnitude amplifier design. The ADC provides 80 dB SFDR for a 20 Mz analog input at 50MSPS while dissipating only 575 mW. Compared to other pipeline ADCs, a two-stage subranging flash architecture minimizes the number of analog and digital pipeline delays, but requires a large number of comparators in the coarse and fine flash converters to implement a high-resolution design. An architecture to implement the coarse and fine A/D converters requires only eleven absolute value or magnitude amplifiers, referred to as magamps, to realize a 12 b 50 MSample/s two-stage sub-ranging ADC. The gain alignment of the coarse and fine converters and the subtraction DAC rely on the statistical matching of the process, and 12 b linearity is obtained without laser trim. The ADC is fabricated on a high-speed dielectrically isolated complementary bipolar process that allows for more than 80 dB harmonic suppression up to an analog input frequency of 20 MHz while keeping the total ADC power dissipation at 575 mW from a single +5 V supply.