[SOLVED] Comment and suggestions of RF amp..

• Dec 17, 2010

• #1

Qube

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Guys i have made this rough design of RF amp,which can amplify 95Mhz frequency...
Please check it once,and please comment and give me some helpful suggestions..
And also check the Pi filter..
Thank u..
Hope u people will help me to increase my knowledge on RF stuff..

 

• Dec 17, 2010

• #2

ckshivaram

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Qube said:

which can amplify 95Mhz frequency...

Click to expand...

How can you amplify a frequency. i think only power can be amplified.

 

• Dec 17, 2010

• #3

Qube

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^^^ sorry typing mistake..
it's actually 95Mhz frequency power amplifier..

 

• Dec 17, 2010

• #4

tony_lth

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What's your simulation results?

 

• Dec 17, 2010

• #5

V

vfone

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This is not a power amplifier. There are two low signal amplifiers placed in cascade. The low pass filter at the output has a cut-off at 75 MHz, and need to be re-designed to allow passing 95 MHz signal. (see the attached picture).

 

• Dec 17, 2010

• #6

Qube

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vfone said:

This is not a power amplifier. There are two low signal amplifiers placed in cascade. The low pass filter at the output has a cut-off at 75 MHz, and need to be re-designed to allow passing 95 MHz signal. (see the attached picture).

Click to expand...

u r absolutely right..
It has limit of 75Mhz..
can u tell me how can i increase it to 95Mhz withould losing the output power..

 

• Dec 17, 2010

• #7

tony_lth

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Use any simulation software, you can tune it.
Just change 100nH to 68nH, and change 100pF to 91pF, the the limit is about 95MHz.

 

• Dec 18, 2010

• #8

Qube

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tony_lth said:

Use any simulation software, you can tune it.
Just change 100nH to 68nH, and change 100pF to 91pF, the the limit is about 95MHz.

Click to expand...

please Check out this onee..
I have made it right..
Now the limit is about 115Mhz..
wat do u think....

 

• Dec 18, 2010

• #9

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vfone

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For Low Pass Filter use 27pF, 130nH, 27pF. After that to get maximum output power from this circuit (without many changes) increase the value of L2 to 1uH, and decrease the value of R6 to 33 ohms.

 

• Dec 19, 2010

• #10

Qube

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vfone said:

For Low Pass Filter use 27pF, 130nH, 27pF. After that to get maximum output power from this circuit (without many changes) increase the value of L2 to 1uH, and decrease the value of R6 to 33 ohms.

Click to expand...

Can u please explain me how u calculated the Low pass filter values as u said..
"For Low Pass Filter use 27pF, 130nH, 27pF"
and also about changing 160nH to 1uH..
It would be a great help if u please explain me how u calculated for this circuit..:smile:

And as per m knowledge,if the value of R6 is reduced tp 33ohms the I(current) will increase and the output power will also increase.please correct me if i am wrong..

 

• Dec 19, 2010

• #11

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vfone

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There are a lot of freeware (or trial) filter design software on the net.

https://101science.com/RFSim99.exe
**broken link removed**
**broken link removed**

For 3dB cut-off frequency chose a frequency about 20% greater than maximum operating frequency, to do not attenuate the useful signal.
Increasing the current on the last stage increase the power, but also change the output impedance. Ideally is to use a non-linear simulator to get the best output power match.

 

• Dec 19, 2010

• #12

Qube

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Thank u very much Vfone..

From a long time i have a simple doubt but not able to solve it and have no one to help me..
I am able to bias a transistor with Resistors..
But in RF amplifier ,I am not able to choose the inductor value @ the collector of the transistor..

can u please please explain me how u select it value..
Take this schematic as example please..

 

• Dec 19, 2010

• #13

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vfone

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The collector inductor of the PA is a choke that sets the collector bias but acts as an open circuit at high frequencies.
In practice the inductance value of the collector choke is not as high as needed for maximum voltage flow. There is a compromise in PA output match design to get both, maximum output power and best efficiency.