CE amplifier ac analysis

[barak198]

Hi everyone
I need some help with CE amp ac analysis ,  I wanted to use the model I added to the circuit
but I am not sure how to find RB ( usually RB1 RB2 are in paralel in ac but not in this case )

thank you all

[HackedFridgeMagnet]

Millers Theorem?  Pretty hazy here, it's been a long time.

https://wiki.analog.com/university/courses/electronics/text/chapter-9

[danadak]

http://www.bu.edu.eg/portal/uploads/Engineering,%20Shoubra/Electrical%20Engineering/2461/crs-11966/Files/ECE312_lec04.pdf

[LvW]

Hi everyone
I need some help with CE amp ac analysis ,  I wanted to use the model I added to the circuit
but I am not sure how to find RB ( usually RB1 RB2 are in paralel in ac but not in this case )
thank you all

In your equivalent small-signal linear circuit all capacitors are assumed to represent short circuits.
For this reason, also in this casae you are allowed to consider R2 in parallel to R3.
The circuit has only DC feedback for operational point stabilization.
However, what is the value for Rc in your equivalent diagram?
And what is the operating frequency (role of C3)?

[orolo]

Note that the amplifier lacks an emitter resistor. If you calculate r_pi, you will get something in the order of 2K, which will dominate the amplifier's input impedance. RB is well over 30K at audio frequencies so, compared to r_pi, it is not that relevant.