BJT noise

BJT noise is calculated from three sources. The thermal noise of Rbb' is calculated from the thermal noise equation given above for resistor noise. The shot noise of the collector and base currents is calculated from the shot noise formula:

$$i_{n}=\sqrt{2.*q*I_{DC}}$$

where q is the electronic charge (1.602e-19 C) and $I_{DC}$ is the DC current in question. The collector and base bias currents can be specified on the MODEL record. If the collector current is not specified it is estimated from the equation for the transconductance parameter:

$$I_{C}=G_{m}*k*T/q$$

where Gm is the transconductance parameter provided for the model. Similarly, if the base bias current is not specified on the MODEL record, the base bias current is estimated from the device $\beta$ which is calculated from the Gm and Rb'e parameters as:

$$\beta=G_{m}*R_{b'e}$$

so that

Ib = Ic / $\beta$.

If the noise contribution from the collector current is not desired, set the collector current equal to a negative value on the MODEL record. If the noise contribution from the base current is not desired, set the base current to a negative value on the MODEL record.