An ultra high speed encoder for 5GSPS Flash ADC

Abstract

In the design of an ultra high speed Flash ADC, a major challenge lies in designing a high speed thermometer code to binary code encoder. In this paper, design of a high speed encoder deploying a new logic design style to convert the thermometer code to binary code with fewer transistors through the use of pseudo-dynamic CMOS logic circuits is presented. With this encoder a much higher conversion rate is achieved when compared to traditional encoders. The sampling frequency can go up to 5GHz with an average power dissipation of 184.8µW. To demonstrate performance, the encoder is implemented in a 4 bit Flash ADC designed in CMOS 90nm technology. The functionality of 4 bit Flash ADC is verified by performing transient analysis and fast fourier transform analysis. The results clearly show that it outperforms commonly used encoders in terms of speed and cost.