Consider a B.IT amplifier in by-passed common-emitter configuration operating wi

Question

Consider a B.IT amplifier in by-passed common-emitter configuration operating with a collector current bias, Ic. Assume that the net collector load is Ro = Rc||Rl- The input potential at the base is vb. Estimate the maximum output voltage swing that might be available at the collector in terms of Ic and Ro. Draw a weakly non-linear equivalent circuit for the B.IT amplifier. Derive expressions for the Taylor Series coefficients (up to third order) in terms of the bias current, Ic, and the emitter junction thermal potential, VT, Assume the current gain Ls high enough that IE ~ Ic.

Explanation / Answer

in case of DC the equation of Vce is ( let Vcc is the supply voltage)

Vce = Vcc - RcI ----------------(1)

if we plot the graph I vs Vce the slope will be -1/Rc .

in case of ac analysis the equation is

vce = - Ic (R0) -------------(2)

so the slope is different.

but the equation (2) must satisfy the quecient point current which is Ic and corresponding quescient voltage =.VceQ

as the slope has changed in case of ac , the X -intercept will change. (let that is Vn)

the distance between Vn and VceQ  = Ic*R0 =  IcR0? = Vd

maximum swing = 2Vd = 2IcR0

Ic = Is(exp(Vbe/VT) -1 )

taylor series expansion

=Is( (Vb/VT) +(Vb/VT?) 2 + (Vb/VT?) 3+(Vb/VT?) 4+......................)

c0 = 0

c1 = Is/VT
c2 =Is/(VT)2

c3 = Is/(VT)3

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