On the current dependence of low-frequency noise in bipolar transistors

The bias dependent characteristics of the base input flicker noise or 1/f noise current generator in bipolar transistors is examined. A simple technique is presented for the determination of the flicker noise magnitude at selected low frequencies with varying collector bias current. The results indicate that the bias dependence of the flicker noise is intimately rated to that of the input conductance parameter gπin the common-emitter configuration. Practical methods are given for the determination of the bias-independent noise parameter ρ0, which, in conjunction with the small-signal network parameters, fully characterize the device noise performance at low frequencies, ρ0, is an equivalent noise resistance representing the open-circuit flicker noise voltage at the base terminal at 1 Hz. Results of noise figure measurements on several representative commercially available devices are compared with those calculated with a knowledge of ρ0.