Theory of Shot Noise in Junction Diodes and Junction Transistors

A theory of shot noise in junction diodes and transistors is presented, based upon a transmission line analogy. The noise is caused by the randomness in the diffusion of the minority carriers and the randomness in the recombination of minority and majority carriers. In transmission line analogy, first process corresponds to distributed noise emf´s in series with transmission line, and second process corresponds to distributed noise current generators in parallel to transmission line. After magnitude of these equivalent distributed noise sources has been determined, noise problem is solved by standard methods. It is found that theoretical results for a junction diode agree with experimental work published earlier. An equivalent circuit describing the noise in transistors is presented. It contains two partially correlated noise current generators ip1 and ip2, ip1, connected across the emitter junction and ip2 connected across the collector junction. (ipi2)av, (ip22)av and (ip1*ip2)av are calculated. At low frequencies emitter and collector current show full shot effect and ip1 and ip2 are almost completely correlated; at higher frequencies the correlation becomes less complete. The noise can also be described by an emf e8 in series with the emitter and a current generator ip in parallel to the collector junction. (e82)av, (ip2)av and (e8*ip)av are calculated. At low frequencies e8 and ip are uncorrelated, but some correlation is expected at higher frequencies. Low-frequency results resemble earlier equivalent circuits of Montgomery, Clark, and van der Ziel, and of Giacoletto.