Bipolar amplifier bias technique for robust IM3 null tracking independent of internal emitter resistance

Balsom, Toby, Redman-White, William and Scott, Jonathan (2012) Bipolar amplifier bias technique for robust IM3 null tracking independent of internal emitter resistance. IEEE 55th International Midwest Symposium on Circuits and Systems (MWSCAS) 2012, Boise, United States. 05 - 08 Aug 2012. pp. 606-609 . (doi:10.1109/MWSCAS.2012.6292093).

Abstract

Bipolar amplifiers can be biased to give a deep null in third order non-linearity, with the potential for high IP3 amplifier stages. This requires maintaining a precise voltage drop across a small resistive emitter degeneration resistance, whose value is related to kT=q. To make such a scheme practical, the bias must not only take into account the change in kT=q with temperature, but must compensate for variations in the degeneration resistance. In this paper we present a bias technique for IM3 null tracking that can take account of temperature and resistance tolerances, and is also insensitive to the value of the internal emitter resistance. Simulations using a 27 GHz BiCMOS technology indicate that the bias of an amplifier can be maintained over temperature, representative element tolerances, and mismatch such that the IP3 performance is maintained within ±9.5 dBV of the optimum null condition. The technique is applicable for a range of bipolar BiCMOS technologies and is attractive for amplifiers where high IP3 is required with moderate noise figure.

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