High-speed SiGe HBT track-and-hold

A wideband track-and-hold (T/H) circuit is developed based on the IBM 7HP SiGe technology with f_t ∼ 120 GHz. A switched-emitter-follower design incorporates features necessary to realize multi-GHz bandwidth and an improved design trade among bandwidth, linearity, and hold-mode feedthrough. Simulations incorporating layout parasitics show the core T/H circuit has a bandwidth of ∼ 4 GHz and an extremely wide sampling aperture bandwidth well beyond 10 GHz. The simulations indicate the T/H has roughly 9-10 - bit performance for linearity and feedthrough level at a signal frequency of 4 GHz. Initial experimental results for the track mode response are also presented. The T/H shows promise for high-speed analog-to-digital conversion and subsampling applications.