Common Base Amplifier Confusion
jm567 - perhaps you have forgotten that the collector current depends on the base-emitter voltage. It is the well-known exponential relation Ic=f(Vbe).
When the base voltage Vb remains fixed and the emitter voltage Ve increases, the voltage difference Vb-Ve=Vbe decreases - and with it the collector current. As a consequence, the collector voltage increases.
Comment 1 (Edit): I like to take the chance for comparing the two possible explanations for controlling the collector current in a common-base stage:
(1) An externally applied RISING signal voltage at the emitter node will REDUCE the voltage Vbe and, therefore, REDUCE the emitter current according to Ie=f[exp(Vbe/Vt)]. Because of Ie=Ib+Ic both currents, Ib and Ic, will also DECREASE by the same exponenetial expression. This is because there is a nearly constant relationship between Ic and Ib (beta).
(2) An externally applied RISING signal voltage will cause a corresponding (small) current change delta(ib) from the emitter to the base (thereby REDUCING the postive DC base bias current +Ib in opposite direction) - however, this small base current change delta(ib) is part of a larger current change delta(ie) because of delta(ie)=delta(ib)+delta(ic).
I think, it is obvious that delta(ib) is NOT the physical reason for delta(ic). All the currents change at the same time due to Vbe change in the same direction.
Comment 2: I must admit that I really cannot understand some parts of the discussion about the &quot;common base amplifier confusion&quot; (title).
The questioner could not see how the collector current will decrease when the voltage at the emitter node of the shown circuit increases (due to an input signal).
Is there any doubt that the transistor will allow an emitter current Ie when the device is &quot;opened&quot; with a voltage Vbe=0.7V and that this current Ie is split into Ie=Ib+Ic? Is there any doubt that this current will be smaller for Vbe=0.65 V ? So - what is the problem? The voltage Vbe=Vb-Ve will be reduced when the emitter voltage Ve is slightly increased due to the input voltage Vi at the emitter node. As a consequence, all three currents (Ie,Ib,Ic) will - according to Ie=Ib+Ic - decrease. Thats all!
I cannot understand why - according to a written comment below - this view should be &quot;misleading&quot;?