How can i calculate the power gain in mosfet amplifiers

Thread Starter

Ghina Bayyat

Joined Mar 11, 2018
112
Can u plaease help me to know how can i calculate the power gain of a mosfet amplifier without having the current gain ??
The power gain formula is Ap = Av * Ai but the current gain of the mosfet is almost infinte and there is no formula to calculate it so how can i find Ap ? Should i just calculate the power dilivered to the load by ohm's low that P= Id ( Rd // Rl ) ? But if the question was find Ap would it be right to find the power on the load ?? I don't think it's right but how can i know Ap ?
 

drc_567

Joined Dec 29, 2008
731
Are you able to measure the current that is going to the load element? Also the load voltage? P=V*I ... same idea at the input node. What waveforms are involved? Maybe you want to look at RMS current and voltage.
 

Reloadron

Joined Jan 15, 2015
4,582
The power gain formula is Ap = Av * Ai but the current gain of the mosfet is almost infinte and there is no formula to calculate it so how can i find Ap ?
Power as expressed in Watts is V * I which is what you have, Voltage multiplied by the Current. In the case of an amplifier and when we state Power Gain I would expect to see the gain expressed as db (decibels). With the basic V * I formula knowing only V or I you can't calculate power so there needs to be more to this?

Just as an example:
Assume that the input voltage is 10 mV (+10 dBm) and the output voltage is 1 V (1000 mV, +60 dBu). The ratio will be 1000/10 = 100, and the voltage gainwill be 20×log 100 = 40 dB. Reference voltage V0 = 1 Volt. Power gain (dB) = 10×log (RF output power / RF input power). The above link will demonstrate power gain.Your formula is how we solve for power and not gain.

Ron
 
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