hi,

can anyone gimme the Solved derivation (or its link/pdf/anything) for the following equation.

__
RE = 25mV
    IE

Also, what is RE and IE anyway?

 

Re is the impedance looking into the emitter of the transistor and Ie is the DC bias current flowing through the emitter.

 

so how's it can be derived?

 

Use the diode equation

I=Io*((expV/VT)-1)

and find dV/dI to get Re

dI/dV=(Io*exp(V/VT))/VT

but Io*exp(V/VT)=I+Io

thus dI/dV=(Io+I)/VT, because Io is very small we ignore it and we get

dI/dV=I/VT

but Re=dV/dI=VT/I=25mV/I, because VT equals about 25mV at room temperature.