High frequency noise figure — A function of fα or fT?
J. W. Thornton · IEEE Transactions on Broadcast and Television Receivers · 1963
There has been some question in the past as to whether fαor fTshould be used as the frequency criterion in determining transistor high frequency noise figure. This report is based on the following equation for noise figure as derived by Nielsen:1$F = 1 + {r_{b}^{\prime} \over r_{g}} + {r_{e} \over 2r_{g}} + {{({r}_g+{r}_{b}^{\prime} + {r}_e)^2} \over {2r_{e}\, r_g \, \beta_o}} \left [1 + {(f/f_a)^2 \over 1-\alpha_o}\right]. \eqno{\hbox{(1)}}$Results show rather conclusively that fαshould be used and not fT, for the frequency range from approximately 40 to 300 mc. These results apply specifically to the diffused base 2N1742 transistor. Conclusions have been drawn by comparing (1) the degree to which theoretical fα-noise figure correlates with measured noise figure to (2) the degree to which theoretical fT-noise figure correlates with measured noise figure