A bootstrap technique for wideband amplifiers

We propose a novel topology for a wideband amplifier, that exploits a series-shunt positive capacitive feedback to compensate the "pole-splitting" action of base-collector capacitance C_μ. Feedback is applied to a buffered differential pair to obtain a bootstrap action; the compensation network requires two capacitors and emitter degeneration resistors in the differential pair, and does not affect biasing and low frequency behavior of the amplifier. We present an AC model of the amplifier to get an insight in the behavior of the proposed compensation technique and to obtain design guidelines for maximizing the gain-bandwidth product. A case study using a 27 GHz-f_T Si bipolar technology has shown a 160% gain-bandwidth enhancement with respect to a simple differential pair, and a 27% enhancement with respect to other topologies proposed in the literature.