A 2.7-V 300-MS/s track-and-hold amplifier

A fully differential bipolar track-and-hold amplifier (THA) employs an open-loop linearization technique compatible with low supply voltage. A feedthrough reduction method utilizes the junction capacitance of a replica switch to provide a close match to the junction capacitance of the main switch. The differential full-scale (FS) input range is 0.5 V. In the track mode, with f/sub in/=10 MHz, FS sinewave input, the measured total harmonic distortion (THD) is less than -72 dB. With f/sub s/=300 MS/s and f/sub in/=10-50 MHz, FS sinewave input, the measured THD is less than -65 dB. This THD measurement reflects the held values as well as the tracking components of the output waveform. With f/sub s/<10 MS/s and f/sub in/=10-50 MHz, FS sinewave input, the measured feedthrough is less than -60 dB. The hold capacitance is 2.5 pF and the differential droop rate is 16 mV//spl mu/s. The THA consumes 32 mW from a 2.7-V power supply and is fabricated in a 0.5-/spl mu/m, 18-GHz BiCMOS process.