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(in) = 10 MHz, FS sinewave input, the measured total harmonic distortion (THD) is less than -72 dB, With f(s) = 300 MS/s and f(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(s) < 10 MS/s and f(in) = 10-50 MHz, PS 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/mu s. The THA consumes 32 mW from a 2.7-V power supply and is fabricated in a 0.5-mu m, 18-GHz BiCMOS process.
