peterpops
Junior Member level 3
Evening!
I'm looking at an example (see figure 1).
They want to know an expression of Rin.
Solution:
"From the figure we see that the voltage vΠ will be equal to -ve. Thus looking between E and ground we see a resistance rΠ in parallel with a current source drawing a current gmve away from terminal E. The latter souce can be replaced by a resistance (1/gm), resulting in the input resistance Rin given by Rin = rΠ // (1/gm)"
I understand the solution, except what the bolded sentence has to do with it. Later there is an exercise with the following figure
Same question, an expression of Rin.
My solution:
Rin = (RB + rΠ) // (1/gm)
However that's not correct...
I see that vΠ is not equal to -ve anymore but how should I solve this one?
I'm looking at an example (see figure 1).
They want to know an expression of Rin.
Solution:
"From the figure we see that the voltage vΠ will be equal to -ve. Thus looking between E and ground we see a resistance rΠ in parallel with a current source drawing a current gmve away from terminal E. The latter souce can be replaced by a resistance (1/gm), resulting in the input resistance Rin given by Rin = rΠ // (1/gm)"
I understand the solution, except what the bolded sentence has to do with it. Later there is an exercise with the following figure
Same question, an expression of Rin.
My solution:
Rin = (RB + rΠ) // (1/gm)
However that's not correct...
I see that vΠ is not equal to -ve anymore but how should I solve this one?