A 25.6-GS/s 40-GHz 1-dB BW Current-Mode Track and Hold Circuit with more than 5-ENOB

A majority of HBT-based track and hold circuits (T/H) with more than 10 GS/s use switched emitter followers (SEFs) as their primary sampling element. The SEFs enable high sampling rates and high analog tracking bandwidths. At high input frequencies, however, they suffer from strong linearity degradations due to base-emitter modulation, signal feedthrough and clock jitter. To address these issues, this work presents a current-mode T/H based on charge sampling. The T/H is implemented in a 130 nm SiGe BiCMOS technology and achieves more than 5 ENOB and more than 33 dBc SFDR up to the 2
^nd
Nyquist frequency at 25.6 GS/s. Time-domain measurements for a 40 GHz input signal are also presented, in which an ENOB of 5.8 and SFDR of 44.6 dBc are achieved.