A 6-Bit 2-GS/s Flash Aanlog-to-Digital Converter in 0.18-μm CMOS Process

A 6-bit flash ADC is fabricated in TSMC CMOS 0.18-μm 1P6M process and supports a sampling rate up to 2 GS/s. The proposed ADC consists of a track-and-hold amplifier, a comparator array, a four-channel ROM-based 64-to-6 encoder, a multiplexer, and a clock generation and distribution system. Instead of traditional latch-based comparators used in high-speed ADCs, continuous-time comparators are employed to minimize kick-back noises and offsets. When the sampling frequency is 2 GHz, the measured SNDR is 30.01 dB at input frequency around 200 MHz. The ADC consumes 255 mW from a 1.8-V supply and occupies 1.88 x 1.92 mm² of die area. In addition to chip implementation, an analysis on resistive averaging network in frequency domain is presented. Characteristics of averaged differential pairs related to input frequency are revealed.