In addition, two different measurement techniques have been evaluated. One is based on the noise figure technique and is considered to be an indirect measurement technique. The second is a direct measurement technique. The second technique has been adopted because it is faster and still provides the noise magnitude at each terminal. First, the collector noise spectra is always greater than the base noise spectra.
Distortion is observed in both collector and base spectra.
This distortion is due to the presence of one or possibly two Lorentz components. One Lorentz component has a corner frequency between 10kHz and 20kHz. The second has a corner frequency beyond 100kHz. Third, the spectra are strongly dependent on the bias current. In contrast, they are only weakly dependent on the collector voltage.