On the design techniques in enhancing gain and bandwidth of bipolar broadband amplifiers

In this dissertation, the circuit topologies and design techniques in enhancing gain and bandwidth of bipolar broadband amplifiers as well as the active bandwidth enhancement techniques for broadband amplifiers have been explored, studied, proposed, and demonstrated. Interestingly, with the innovations in circuit topologies and design techniques, this dissertation will demonstrate that one can achieve broadband amplifiers with higher gain-bandwidth products than others even if all have used the same transistor technology, 2 um InGaP/GaAs Heterojunction Bipolar Transistors, in the designs.; The dissertation begins with the proposed modified gain cell in enhancing amplifier gain-bandwidth product. Then, four different broadband amplifiers are proposed and demonstrated. The Traveling Wave Matching (TWM) broadband amplifier, an alternative solution providing good gain and wide bandwidth with low power consumption and alleviating input and output broadband matching issues, achieves 7.5 dB gain and the 23 GHz of 3-dB bandwidth with low do power consumption of 20 mW.; The HBT distributed amplifier implemented with proposed modified gain cells has demonstrated superior gain-bandwidth product over the TWM broadband amplifier with the gain of 15.3 dB and 32 GHz of 3-dB bandwidth.; The novel HBT matrix amplifier with the proposed modified gain cells achieves a gain of 17.3 dB and 41 GHz of 3-dB bandwidth, representing a gain-bandwidth product of 297 and superseding the distributed, and TWM amplifiers, and occupies a chip area of 1.5 x 1.6 mm2.; Comparing to other published results using the figure of merits of both amplifier gain-bandwidth products per transistor ft and per f max, the measures of design techniques in enhancing amplifier gain-bandwidth products, the distributed and matrix amplifiers in this dissertation are among the best reported single chip distributed and matrix amplifiers implemented in any bipolar technologies. To the best of our knowledge, the matrix amplifier implemented with the proposed modified gain cell in this work, achieving 4.71 and 4.43 in GBP per transistor ft and fmax respectively, is believed to achieve a new benchmark among the ever reported results.; Finally, an active bandwidth enhancement technique employing an active inductor (bipolar transistor) as a gain peaking element for cascode amplifier is firstly demonstrated with 91% in bandwidth enhancement as compared to the bandwidth of cascode amplifier itself. A single-stage cascode amplifier with the active inductor as a tunable gain peaking element achieves 6-dB gain with adjustable bandwidth from 8.5 to 16.2 GHz. To the best of our knowledge, this is believed to be the first time demonstrating the usage of the active inductor as a gain peaking element for broadband amplifier application beyond 16 GHz with a large percentage of bandwidth enhancement and wide tuning frequency range.