Electronics > Projects, Designs, and Technical Stuff
basic transistor amplifier
ykurban:
How do you calculate gain of this simple amp?
schmitt trigger:
Are you familiar with a bipolar transistor's h-parameters?
Since most resistors are well bypassed with capacitors, at a mid-frequency the circuit is reduced to a grounded emitter with a single collector resistor load.
Although you can calculate the gain of the stage by itself, for the actual gain you require to know the load impedance and the source impedance.
graybeard:
If you can assume beta is large then the base voltage is:
VB = R8 / (R8 + R9 + R10 + R11) * 9V = 2.96V
The emitter voltage is:
VE = VB - VBE = 2.96 - 0.68 = 2.28V
The emitter current is therefore:
IE = VE / R12 = 84µA
since we assumed beta is large:
IC = IE
the transistor transconductane is:
gm = IC / VT = 3.36 mS
where VT = k * TK / q = 25mV
the mid band voltage gain from the base to the collector is:
AV = gm * R4 = 3.36ms * 2.2KOhms = 6.72
As schmitt trigger said the load and source impedances will alter this result.
duak:
Graybeard, I remember doing those calculations in college and was able to determine the DC conditions. I remember the next steps used IE and the 25 (or 26 mV) constant but not that it gave the transconductance. Use it or lose it, indeed.
graybeard:
--- Quote from: duak on April 09, 2020, 04:44:14 pm ---Graybeard, I remember doing those calculations in college and was able to determine the DC conditions. I remember the next steps used IE and the 25 (or 26 mV) constant but not that it gave the transconductance. Use it or lose it, indeed.
--- End quote ---
In my case it has been more than 30 years since I taught this as graduate assistant, but I still use it for work.
Navigation
[0] Message Index
[#] Next page
Go to full version