Design of 4-Bit Flash ADC using TIQ based Comparator

Abstract

Analog-to-digital converters are the key components
in modern electronic systems. Since signal processing in digital domain has widely being studied, designing an analog-to-digital converter has become more challenging for the researchers. In this
paper, a novel flash analog-to-digital converter for low-power & high speed applications has been proposed by incorporating the threshold inverter quantization technique. The key idea of this technique is to generate 2n – 1 different sized threshold inverter quantization comparators for an n-bit converter due to which the fast data conversion speed improves the operating speed and the elimination of ladder resistors leads significant reduction in the power consumption. The use of two cascaded inverters as a voltage comparator is the
reason for the technique's name (TIQ). The voltage comparators compare the input voltage with internal reference voltages, which are determined by the transistor sizes of the inverters. Hence, we do not need the resistor ladder circuit used in a conventional flash ADC.
Unlike the conventional flash ADC whose comparators are all
identical in size, the TIQ based ADC has individual comparators in all different sizes. To construct an n-bit flash TIQ based ADC, one must find 2n- 1 different inverters, each has different Vm value, and
one must arrange them in the order of their Vm value. The gain boosters make sharper thresholds for comparator outputs and provide a full digital output voltage swing. The comparator outputs - the
thermometer code - are converted to a binary code in two steps through the `01' generator and the encoder. The proposed 4 bit flash ADC using TIQ is designed using FAT tree encoder and simulated
with the help of TANNER-EDA tool in 0.25 μm CMOS technology.