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In this paper, we present the analysis and design of a charge sampling amplifier (CSA) in 90 nm CMOS for medical imaging applications. The CSA is designed based on a 1 V CMOS folded cascode operational transconductance amplifier (OTA) with lead compensation. The OTA achieves a DC gain of 45-dB and a unity gain frequency of 1.3 GHz at a power consumption of 200 muW. Performance of the charge sampling amplifier is investigated when it is connected to a single capacitive micro machined ultrasound transducer (CMUT). The proposed CSA front end architecture for ultrasound imaging achieves a transfer gain of 19 dB from CMUT signal source to the output of the CSA (across feedback capacitor) with sampling simultaneously.