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two stage UHF ampliefier - wideband interstage matching

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maniana

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ampliefier

Hi,
I design a two stage UHF amplifier, 2Watts.
I have a problem two achieve a wideband interstage matchig.
The optimum output impedance of the first stage is R=U^2/2P => R=100 ohm
while the optimum input impedance of the second stage is only 4 ohm. With such a large impedance ratio it is very difficult to achieve wideband matching.

I was wonder whether someone nows techniques of achieving wideband impedance transformation in such cases.
( I don't wont to wind any transformers and I would prefer to have the same supply voltage for both stages).
 

two stage UHF ampliefier

It is possible but I have one question.
Are you sure that input impedance of the second stage is only 4 ohm only.
 

Re: two stage UHF ampliefier

Hi,
second stage input impedance is exactly = 4.88 +j6.34
first stage output impedance , I don't remember exactly but it is something like 96-j40
both values as seen towards the corresponding device
12V Vdd for both devices, 100mW output power of the first stage, 2W output power of the second stage, Fcentre=440MHz
 

two stage UHF ampliefier

The data sheet of the final amplifier gives application circuit that matches to 50 ohm.
Now you can try for 100 to 50 ohm i.e. first stage output to the circuit given in the application note.
 

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