A 5-b 10-Gsample/s A/D Converter for 10-Gb/s Adaptive Optical Equalizers

A 5-bit flash A/D converter (ADC) is developed in a 0.18-mum SiGe BiCMOS that supports sampling rates of 10-Gsamples/s. The ADC is optimized to operate in digital equalizers for 10-Gb/s optical receivers, where the ADC has to deliver an effective number of bits (ENOB) greater than three with input frequencies well beyond Nyquist. A fully differential flash ADC incorporating with a wideband track-and-hold amplifier (THA), a differential resistive ladder, as interpolation technique, and a high-speed comparator design is devised to resolve the aperture jitter and metastability error. The ADC achieves better than 4.1 effective bits for lower input frequencies, and 3 effective bits for Nyquist input at 10-GS/s. The ADC consumes about 3.6 W from -3.7/-3 V dual power supplies at 10-GS/s, and occupies 3x3 mmsup2 of chip area.