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Common-Base Amplifier. Common-Base Amplifier. Response of CB Stage to small Change in Input Voltage. Input Impedance. Application of CB Stages. Response to a Source of Finite Source Resistance. Output Impedance. Input Impedance. General CB. ( VA=infinity, RB>0 ).
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General CB (VA=infinity, RB>0) Resistance seen by the input Base resistance (RB) decreases voltage gain.
CB Stage with Biasing X to Vout
Design Goal Goal: i2>>i1
Bypass Capacitor (Base resistance decreases gain!) It is therefore desirable to have a bypass capacitor!
Design Guideline • Given: Rin, AV • Select RE>>(1/gm). • gm →IC. • RE=10Rin • Av=gmRC →RC • Vb=IERE+VBE • Let I(R1)=40IB →(R1+R2) • R2 is known from Vb and R1. • 1/(C1ω)=(1/gm)/20 • 1/(beta+1)/(C1 ω)=(1/gm)/20