Fat tree encoder design for ultra-high speed flash A/D converters

The thermometer code-to-binary code encoder has become the bottleneck of ultra-high speed flash ADCs. In this paper, the authors present the fat tree thermometer code-to-binary code encoder that is highly suitable for ultra-high speed flash ADCs. The simulation and the implementation results show that the fat tree encoder outperforms the commonly used ROM encoder in terms of speed and power for the 6 bit CMOS flash ADC case. The speed is improved by almost a factor of 2 when using the fat tree encoder, which in fact demonstrates the fat tree encoder is an effective solution for the bottleneck problem in ultra-high speed ADCs.