# Output power, Drain Current versus multipliers

1. ## Output power, Drain Current versus multipliers

Hi, I set Width(W) and Number of fingers (nf) for a transistor (in CS configuration) and found out it's drain current (Id) and output power (Pout)(Using HB simulation) for a particular load resistance(R). Now, If I want the output power 8 times that of Pout, is it just enough if I take 8 multipliers without changing R ? and does that mean Drain current (Id) is also increased by 8 times?.

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2. ## Re: Output power, Drain Current versus multipliers

Can you surely understand "Instance Multiplier" ?

Originally Posted by circuitslave
If I want the output power 8 times that of Pout,
is it just enough if I take 8 multipliers without changing R ?
No.

Can you surely understand "Impedance"and "Power" ?

Show me your definition of input power.

Originally Posted by circuitslave
and does that mean Drain current (Id) is also increased by 8 times?.
No.
Surely consider operation point, input and output impedance.

Surely learn and understand followings.

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3. ## Re: Output power, Drain Current versus multipliers

You would get 8 times the drain current at DC no doubt. Now imagine you have managed to bias everything in class A. Then your current swing will be 8 times higher. 8 times current swing x same R --> ideally you should get 8 times the voltage swing. But you will be limited by your supply voltage. Typically, a PA is designed such that at the peak point, your voltage swing amplitude equals the supply voltage (I assume you have used an inductance between the drain and supply). So for the same resistance, you will not get 8 times the voltage swing. You will clip and will end up with power in higher harmonics.
So, you need to change your input matching network so that you see 8 times lower resistance.
But that is not the end of it. Now because your transistor is 8 times larger, your capacitance will increase as well. For optimum power matching, you need to change the value of the capacitance and inductance.

In short, the answer is NO. Resources pointed out by pancho_hideboo are really excellent and you should go through them.

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