Low-frequency noise modeling of bipolar junction transistors for VLSI circuits

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Abstract
This paper presents results of an experimental study on the input referred current noise SI variation with emitter area A of bipolar transitors. In the study, seven bipolar transitors in which the emitter area varied from 1.6 μm2 to 144 μm2 were used and the noise measurements were done at 293 K and 313 K. The experimental results were modelled using the expression SI(f)=KF*1AF/f which is the bipolar junction transistor flicker noise model used in HSPICE. The goal of our works is to investigate how these HSPICE noise parameters vary with the emitter area. From our experiments, the parameters AF was found to be weakly dependent on the emitter area. From our experiments, the parameter AF was found to be weakly dependent on the emitter area with values from 1.4 for the largest device to 1.9 for the smallest device at both temperatures. Reducing the emitter area by 2 orders does not increase the dependence of AF on the base current significantly. However, the parameter KF was found to be strongly dependent on the emitter area a both temperatures with values from 3E‐15 for the largest device to 3.1E‐10 for the smallest device and was found to increase approximately as the square of the inverse of the emitter area. KF was found to be approximately proportional to 1/A2.21±0.17 at 293 K and proportional to 1/A1.83±0.30 at 313 K where A is the emitter area. This experimental finding has a significant effect on the noise performance of BJTs, for example, a reduction in emitter area by 3 results in almost an order of magnitude increase in the current noise power.

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