Spo. Bruce et al., Measurement of low-frequency base and collector current noise and coherence in SiGe heterojunction bipolar transistors using transimpedance amplifiers, IEEE DEVICE, 46(5), 1999, pp. 993-1000
Transimpedance amplifiers have been used for direct study of current noise
in silicon germanium (SiGe) heterojunction bipolar transistors (HBT's) at d
ifferent biasing conditions. This has facilitated a wider range of resistan
ces in the measurement circuit around the transistor than is possible when
using a voltage amplifier for the same kind of measurements. The ac current
amplification Factor h(fe) and the sum of the base and emitter series resi
stances (r(b) + r(e)) have been extracted from the noise. It has been estab
lished that the dominant noise source is situated in the base emitter junct
ion at the emitter side and is not related to contact resistance noise. The
simultaneous measurement of both the base lead noise and the collector-lea
d noise and the calculation of the coherence between the signals has facili
tated the pinpointing of the dominant noise source in the device and the ex
traction of (r(b) + r(e)).