[Qucs-help] BJT noise model From: Markus Mettenleiter <3m@zo...> - 2007-10-08 17:32 ```Dear QUCS team, =20 first of all, congratulations and my very respect for your ambitious project! I particularly like the concise compilation of all the models and the math behind SPICE, you are providing. =20 Since I'm currently dealing with BJT noise (in a very low noise TIA application), I had a closer look at the BJT noise model (fig. 10.15) and related equations. The noise sources ib^2 and ic^2 from equations 10.145 and 10.146 are very clear to me, but how do the contributions of the ohmic resistances Rbb, Rc, Re (equ. 10.144) fit into the figure 10.15 noise model ? None of the terms shows up there, but at least Rbb can not be neglected for a decent noise calculation. =20 To my knowledge the noise contribution of Rbb can be regarded as voltage source with ubb^2 =3D 4KTRbb and placed in series with Rbb of figure 10.10. But what about the noise contributions of Rc and Re - convert them into voltage sources and place them in series with Rc and Re of the figure 10.10 model as well ? However, it's not quite clear from this document, what the simulator actually calculates.... =20 So could you please enhance the fig. 10.15 noise model with the Rbb, Rc, Re noise sources - or let me know what I overlooked ! =20 (btw.: the very similar questions arise regarding the FET- and Diode- noise models.) =20 =20 Best regards, Markus Mettenleiter (R&D engineer) ```
 Re: [Qucs-help] BJT noise model From: Stefan Jahn - 2007-12-29 12:31 ```Am Mo, 8.10.2007, 18:31, schrieb Markus Mettenleiter: > Dear QUCS team, Hi! And sorry for the very looooong delay. > Since I'm currently dealing with BJT noise (in a very low noise TIA > application), I had a closer look at the BJT noise model (fig. 10.15) > and related equations. The noise sources ib^2 and ic^2 from equations > 10.145 and 10.146 are very clear to me, but how do the contributions of > the ohmic resistances Rbb, Rc, Re (equ. 10.144) fit into the figure > 10.15 noise model ? None of the terms shows up there, but at least Rbb > can not be neglected for a decent noise calculation. > > To my knowledge the noise contribution of Rbb can be regarded as voltage > source with ubb^2 = 4KTRbb and placed in series with Rbb of figure > 10.10. But what about the noise contributions of Rc and Re - convert > them into voltage sources and place them in series with Rc and Re of the > figure 10.10 model as well ? However, it's not quite clear from this > document, what the simulator actually calculates.... The noise current in parallel to the resistances Rbb, Re and Rc are computed as 10.144 states. The figure 10.15 leaves them, because it only shows the "intrinsic BJT". > So could you please enhance the fig. 10.15 noise model with the Rbb, Rc, > Re noise sources - or let me know what I overlooked ! Well, I think it's so very easy, that we decided to leave that. I am not yet unsure if I should really add these... Cheers, Stefan. ```