Seyyed Sajjad Mortazavi - Msc Student, Department of Electrical Engineering, Imam Reza International University, Iran,
Samaneh Babayan-Mashhadi - Assistant Professor, Department of Electrical Engineering, Imam Reza International University, Iran,

One of the most important analog circuits required in many analog integrated circuits is comparator. design of comparator becomes an important issue when design technology and supply voltage is scaled down. Due to the non-linear behaviour of threshold voltage (VT) with the advancement of CMOS technology, performance of comparator is most affected. Many versions of comparator are proposed to achieve desirable output in sub-micron and deep sub-micron design technologies. One of the ways to overcome the challenge of low-voltage design is to process a signal in the time-domain. Time resolution has been improved in nanometer-scale devices due to the reduction of gate delay, despite the reduction in supply voltage. Hence, time-domain processing potentially offers a better solution compared to voltage-based methods, when implemented in deep sub-micron VLSI fabrication processes. This paper presents a comparative review of different types of time-domain comparators. Also all mentioned types of comparators are analyzed on the basis of different characteristics and sources of error in this comparators and their reduction technique is discussed.

time-domain comparator, low-power and low-voltage designs, ladder-based comparator, differential time-domain comparator