i have to design a power amplifier which works at 13.56mhz and gives an output power around 1 watt. i am confused which class to choose c , d ,e ?? please help me to design it.

 

Are you amplifying a modulated 13.56MHz carrier or is this a simple continuous wave RF amplifier?

 

I would suspect that at those power levels and frequencies it might not matter too much unless you have some requirements which you have not articulated. Getting rid of 1 Watt of heat is not too difficult with a garden variety heatsink.

 

the output power should be 1 watt and this amplifier i have use for medical application. the input current is 100 mA and i want out current of around 1.15 A. which configuration is the best C , D or E.

 

Also it not modulating... its simple RF amplifier

 

the output power should be 1 watt and this amplifier i have use for medical application. the input current is 100 mA and i want out current of around 1.15 A. which configuration is the best C , D or E.

So you're not driving a 'standard' 50Ω load. Are you driving some sort of inductive loop? Perhaps you could elaborate your requirements a little more.

 

i attached a picture I have make the pA in the given foto. please have a look.

 

So you're not driving a 'standard' 50Ω load. Are you driving some sort of inductive loop? Perhaps you could elaborate your requirements a little more.

There is a minor problem. 1 Watt of output power at 1.15 A will mean a very low output voltage of perhaps 0.87 Volts (RMS?). Designing things like power amplifiers at such low voltages is well tricky to say the least. You will have trouble biasing your output stage. Gain of 10 is not unreasonable. It might make more sense if you designed for say 15 Watts of output power. Then you would have 13 V @ 1.15 A

 

i am new to this i have no idea how to design can u tell which class should i opt for and also some good book where i can learn how to design an power amplifier from basics.

 

There is a minor problem. 1 Watt of output power at 1.15 A will mean a very low output voltage of perhaps 0.87 Volts (RMS?). Designing things like power amplifiers at such low voltages is well tricky to say the least. You will have trouble biasing your output stage. Gain of 10 is not unreasonable. It might make more sense if you designed for say 15 Watts of output power. Then you would have 13 V @ 1.15 A

While an inductive loop arrangement isn't likely to radiate much in terms of far field, I think a 15 W level would not be permissible for the ISM band - which I believe includes 13.56MHz.

 

i want for ISM band only ....can u suggest which class to use .. or some books with basics i went through steve cripps book on rf power amplifiers for wireless communication. its going above my head . can you suggest some basic book on power amplifier design.

 

I would use a class C amp, it is fairly efficient, but not generally suitable for modulation.

13.56Mhz is a frequency set aside internationally for this kind of use. My work uses something very similar at that freq for plasma ashers, which operate between 100-400Watts. When I sprained my ankle around 20 years ago they used the RF to warm my tissue in my ankle to speed healing, it was around 5 - 10W.

The main thing you need to worry about is harmonics, you do not want multiples of this frequency broadcasting.

 

Thnkx for the suggestion Bill_Marsden. I research and I came to a conclusion either class C or Class E should be used.I have got many paper which use class E amplifiers for 13.56 MHz and they also say Class E easier to design and that in class C the output power reduces as conduction angle is decreased (which is done to increase the efficency).
And also efficency wise class E better than C but i dont know if this switching mode can be used for my application. I am not looking for linearity.I am confused between clas E and C what to use.
one of the book says:

Class E has disadvantage about in terms peak voltages.. it goes 3.5 VDD compared class C which goes upto 2 vdd

.
wht does this mean??

 

hi katrina, wonder if your power amplifier is up already?