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| 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. |
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