A current-based close loop track-and-hold circuit with a speed of 50 MS/s and 8-bit resolution for plusmn0.8 V input range is implemented using a voltage-control current source and a current switch. The proposed circuit has the advantage of high input impedance and stable output. SPICE simulation using 0.35 mum SMIC CMOS technology with plusmn1.65 V supply showed that the proposed track-and-hold circuit has good input tracking capability, small linear gain error, and can work at high sampling rate.