A 5-b 10-GSample/s a/D converter for 10-gb/s optical receivers

A 5-b flash A/D converter (ADC) is developed in an 0.18-μm SiGe BiCMOS that supports sampling rates of 10 Gsample/s. The ADC is optimized to operate in digital equalizers for 10-Gb/s optical receivers, where the ADC has to deliver over three effective number of bits (ENOBs) at Nyquist. A fully differential flash ADC incorporating a wide-band track-and-hold amplifier (THA), a differential resistive ladder, an interpolation technique, and a high-speed comparator design is derived to resolve the aperture jitter and metastability error. The ADC achieves better than 4.1 effective bits for lower input frequencies and three effective bits for Nyquist input at 10 GS/s. The ADC dissipates about 3.6 W at the maximum clock rate of 10 GS/s while operating from dual -3.7/-3V supplies and occupies 3×3mm² of chip area.