Thermometer code to Binary code Converter for Flash ADC - A Review

Flash ADC is the fastest analog to digital converter, also known as parallel ADC. It is ideal for applications requiring large bandwidth. It consists of a resistor ladder, comparator and an encoder circuit. Output of the comparator is a thermometer code. It has to be converted to corresponding binary code using suitable encoder. Decreasing power dissipation of an encoder is a major concern while designing low power Flash ADC. This paper compares various encoder circuits such as ROM encoder, fat tree encoder, Wallace tree encoder and MUX based encoder. Even though fat tree encoder is the fastest encoder, it is more complex in structure. This makes the layout design difficult. Wallace tree encoder is best in terms of bubble error correction, but it consumes more power. Among these multiplexer based encoder is more power efficient and simple in design. So it is more suitable for low power Flash ADC design.