A fast, latching comparator for 12 bit A/D applications

High-speed, 12 bit accurate successive approximation A/D converters demand a comparator with both excellent input specifications and fast response time. The author describes a voltage comparator with 50 ns response time to 1/2 LSB overdrive (1.2 mV) and 0.1 LSB (250 /spl mu/V) total input error. Unique features of the circuit include a super-/spl beta/ input stage, a fast buried-zener level-shift, a fully differential output stage, a floating-zener biasing scheme, and a fast latch circuit which does not interfere with input accuracy. The comparator is manufactured on a bipolar, double-implanted, thin epi, junction-isolated process.