30 June 2005 A 40-Gb/s driver circuit using a novel inductive bandwidth extension technique
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Abstract
A positive feedback technique is proposed to augment the bandwidth extension achievable using peaking inductors. The technique is based on inductor sharing between consecutive amplifier stages, and it can be effective when used with smaller inductance values compared to traditional inductive peaking. A 40Gb/s two-stage amplifier comprising a differential pair and emitter followers is presented as a practical design example. An expression for the transfer function of the proposed circuit is derived, and its bandwidth and group delay are compared to equivalent amplifiers with inductive peaking and without bandwidth extension. Circuit sensitivity to the inductance value is also considered. The proposed amplifier was implemented in a SiGe BiCMOS process with ƒτ=120GHz and is used as a predriver for a 50Ω buffer. Combined with the buffer, it provides 10dB of gain and consumes 90mW from a 2.5V power supply and 180mW from a 3.3V power supply. Simulations show about 40% bandwidth improvement compared to traditional inductive peaking. Time domain measurements demonstrate 40Gb/s operation with a maximum differential swing of 1.0V p-p and 20-80% transition times of 7-9ps.
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Daniel Kucharski, Kevin T. Kornegay, "A 40-Gb/s driver circuit using a novel inductive bandwidth extension technique", Proc. SPIE 5837, VLSI Circuits and Systems II, (30 June 2005); doi: 10.1117/12.608543; https://doi.org/10.1117/12.608543
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