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On the oscillation limits of HBT cross-coupled oscillators

Published online by Cambridge University Press:  16 February 2012

Atheer Barghouthi
Affiliation:
Chair for Circuit Design and Network Theory, Dresden University of Technology, Helmholzstrasse 18, 01069 Dresden, Germany. Phone: +49 351 463 32702
Corrado Carta
Affiliation:
Chair for Circuit Design and Network Theory, Dresden University of Technology, Helmholzstrasse 18, 01069 Dresden, Germany. Phone: +49 351 463 32702
Udo Jörges
Affiliation:
Chair for Circuit Design and Network Theory, Dresden University of Technology, Helmholzstrasse 18, 01069 Dresden, Germany. Phone: +49 351 463 32702
Frank Ellinger*
Affiliation:
Chair for Circuit Design and Network Theory, Dresden University of Technology, Helmholzstrasse 18, 01069 Dresden, Germany. Phone: +49 351 463 32702
*
Corresponding author: F. Ellinger Email: frank.ellinger@tu-dresden.de

Abstract

In evaluating the potential of a given integrated-circuit technology, the negative conductance approach is used to estimate a maximum frequency limit for the ability of Heterojunction Bipolar Transistor (HBT) cross-coupled architecture to function as an oscillator at high frequencies. In this paper, the simple low-frequency estimation of the negative conductance, commonly used in the literature, is extended by deriving a new expression that takes into account the HBT parasitics. An expression for the frequency at which the negative conductance of the circuit crosses zero is given, which gives maximum frequency of oscillation for an ideal tank (no tank losses). In addition, the effect of the feedback capacitor, which is commonly added for direct current (DC) decoupling and boosting the negative conductance, is analyzed and new insight on the choice of the value of this capacitance is introduced. The results were proven by simulations using SiGe HBT transistors with an ft of 190 GHz.

Type
Research Papers
Copyright
Copyright © Cambridge University Press and the European Microwave Association 2012

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References

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