# How to calculate the amplification of a common basis stage

Discussion in 'Electronic Basics' started by Geir Klemetsen, Nov 17, 2003.

1. ### Geir KlemetsenGuest

I know all the values, included the hfe for T1. And it's the voltage
amplification I want to find.
I'm loking for a formula to calculate it (not measure the input and
output).

Here is the schematic:
(Best seen using fixed font Eg. Courier)

+Ucc
.-----------------o------------o
| |
| |
.-. .-.
| |R1 | |R3
| | | |
'-' '-'
| | || V~out
| o-----||-----o
| | ||
| | C2
| |/
.----o--------------|| T1
| | |>
| | |
| | | || V~in
| | o-----||-----o
| | | ||
| .-. .-. C3
C1 --- | |R2 | |R4
--- | | | |
| '-' '-'
| | |
| | |
'----o-----------------'
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

2. ### BaphometGuest

Try this: http://www.tpub.com/content/neets/14179/css/14179_86.htm

3. ### BaphometGuest

I should have added Google [ calculate gain common base transistor ]

4. ### John LarkinGuest

Assuming all the caps are big enough, Vin drives the emitter
resistance of T1 (which should actually be Q1... 'T' means
'transformer') , whose small-signal impedance is about re = 26/Ie, Ie
being emitter DC current in milliamperes. So we now know the AC
current into the emitter (factor in a bit of current lost into R4, if
you're compulsive.) Now most of that (we lose a bit to the base from
finite beta) shoots out the collector into R3 and becomes the AC
voltage output.

OK?

John