Abstract- Analog-to-Digital Converters (ADCs) translate the analog quantities into digital language, used in information processing, computing, data transmission and control systems. ADCs are key components for the design of power limited systems, in order to keep the power consumption as low as possible. Implantable Medical electronics, such as Pacemakers and cardiac defibrillators are typical examples of devices where ultra-low-power consumption is paramount. This paper presents the design of CMOS comparator based on a preamplifier circuit. The design is intended to be implemented in for Analog-to-Digital Converter (ADC). The design is simulated in 1 μm CMOS Technology with HSPICE. Proposed design exhibits low power consumption. Simulation results are presented and the design has DC Gain of 68dB, the power dissipation of 1.25 mW at 5 V.