Transistor noise at high injection levels

Measurements of transistor noise at high injection levels are compared with the predictions made by the low-level injection theory, The noise is represented by an emf eein series with the emitter and a current generator i in parallel with the collector: eeis split into a part ee\´ fully correlated with and a part ee" uncorrelated with . The measured values of usually agree very well with theory, even at high currents; this indicates that the low-level injection theory of remains correct at high injection levels. The measurements of , though inaccurate, seem to indicate that the predictions made by the low-level injection theory are approximately correct at high injection levels. The measurements of the cross correlation indicate a large discrepancy with the low-level injection theory. The theory predicts that is quite small at low frequency and is mainly imaginary at high frequencies. The measurements indicate that is quite large at low frequencies and that its real part is larger than the imaginary part at high frequencies. The fact that varies as , so that it approaches zero at low currents, indicates that it is a high-level injection effect.