Comparators are mostly used in Analog-to-Digital Converters (ADCs). In the conversion process, first the input signal is sampled. Then the sampled signal is applied to a number of comparators to determine the digital equivalent of the analog value. Apart from that, comparators are used in peak detectors, zero crossing detectors and switching power regulators. Different types of comparators are studied and the circuits are simulated in LTSpice-IV using PTM 45nm technology. The circuits are simulated with 1V DC supply voltage.