A high linearity, 8-GSa/s track-and-hold amplifier in GaAs HBT technology

摘要

A high linearity full differential 8 GSa/s track-and-hold amplifier (THA) is presented in this paper. The proposed THA is designed and implemented using 2-μm GaAs HBT technology to be targeted for faster operation in sampling systems at a clock frequency of GHz. In this THA, an alternative switch emitter follower (SEF) is used as a switching stage with a Schottky diode for hold-mode isolation enhancement and high-speed operation. In conjunction with well-designed input buffer allows us to achieve high linearity and comparable dynamic performance. Measured small signal ?3 dB bandwidth, and hold-mode isolation are better than 3.6 GHz and 40 dB, respectively. The prototype achieves a spurious-free dynamic range (SFDR) of 43.9 dB at 0.5 GHz and an average total harmonic distortion (THD) below ?40 dBc up to a first Nyquist frequency of 4 GHz. This work has the potential for wideband, high speed and low distortion analog to digital converter (ADC) used in the future direct sampling systems.