This paper presents a low power, low noise preamplifier stage with simple common mode desensitization circuit for dynamic comparators. The target application of the proposed circuit is analog to digital converter for biomedical applications. Adopting TSMC 0.18μm technology, the proposed circuit is designed to work in weak inversion using gm/ID design methodology. The simulation results show that the preamplifier stage consumes less than 32nW using power supply of 0.75V. The input referred noise is 17μV, DC gain of 43.15dB and unity gain frequency of 300 kHz