vbe multiplier circuit
The Vbe multiplier is used to avoid the dead zone in the output stage of an amplifier.
The problem is that due to the Vbe of the two transistors in the output stage, there is a dead zone, and for some reason's you don't want tihs.
To avoid this the idea is to put an aditional 2*Vbe betwen the bases of the output stage transistor, this is made with a Vbe multiplier.
To choose the values you first must ensure that an enought current is provided to the Vbe multiplier by the polarization.
Supose you are using an NPN transistor with a Vbe(on) = Vbe, and two resistors, R1 and R2, where R1 is connected betwen the base and the colector; and R2 is connected betwen the base and the emiter.
The current flowing thru R2 is I_R2=Vbe/R2, so the voltage in R1 is V_R1=I_R2*R1 (Asumming Ib<<I_R1 and I_R2), in this case you obtain a total voltage betwen the emiter and the colector of the transistor of Vce = V_R1+Vbe where V_R1=(Vbe*R1)/R2, so: Vce = Vbe + Vbe*(R1/R2).
I hope this can help you, and excuse my not so good english.
Bye and gook luck