Design of a low power flash ADC using threshold inverter quantization technique in 90nm technology

All the signals are analog in nature. An analog to digital converter plays an important and essential role for system-on-chip (SOC) applications because it bridges the gap between the analog physical world and the digital logical world. Now a days low power and low voltage requirements becoming more important issues as the channel length of the MOSFET shrinks so below levels. For improvement of power and speed in an analog to digital converter major building block is a comparator. This paper presents a design of 4-bit low power flash ADC for system-on-chip applications using Threshold Inverter Quantization (TIQ) comparators. The technique threshold inverter quantization uses two cascaded CMOS inverters as a comparator, that eliminates the requirement of resister or capacitor ladder circuit. Threshold inverter quantization provides high speed, low power, and smaller area. TIQ also eliminates the requirement of high gain differential input voltage comparator that are inherently more compound and slower than digital inverters. TIQ based flash ADC also eliminates the need of reference voltages, which require a resister ladder circuit. In the TIQ based flash ADC the reference voltage is internally generated by the circuit that is threshold voltage is used as a reference voltage for comparing the input voltage and produce the thermometer code. An efficient thermometer to binary converter has been designed using transmission gate based on 2*1 multiplexer. Power consumption reduced as per accordance to threshold voltage and for high speed transistor size must kept small. The TIQ based flash ADC requires 2n-1 comparators, where n is the number of bits or resolution. To reduce the power consumption of the design, the threshold voltage should not be deviated too much and keep WP/Wn < 1 to reduce power consumption and paracitic capacitance.