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RF transformer/amplifier

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Aug 18, 2009
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transformer amplifier

Hi, i'm currently working on an RF amplifier, on which i currently don't have the schematic on the computer i'm using now. But basically, it looks like the circuit over here: , except that after the transistors it goes directly to a transformer and then output. I am using OrCAD to simulate it right now, and i'm having trouble with simulating the transformer(as the manufacturer refuses to give me some information, the only information available are ohm ratio, freq range, insertion loss and input r. loss). How do you think i can get around this?and also i'm looking for a transistor (FET especially) for my circuit. The frequency range is 0-300Mhz. i am using blf202 but i can't get the orcad library/model for it. Is there any suggestion of what transistor i can use?and by the way, both transformer are tt4-1a+ by minicircuits. Thanks

rf transformer

In Minicircuits datasheet is specified Ratio 4, that means is a 4:1 transformer.
I didn't use Orcad for a while but I think in the library is a 4:1 transformer that you can use.
If you do not have the Spice model for BLF202 try to find in the library an available lower power MOSFET (same frequency range), and use it just to see how the simulation works at low signal level.

transformer ohm ratio

but when it says ohm ratio is 4 means the ratio of secondary/primary?

Added after 4 minutes:

and also, is there any way to get .olb and .lib file for orcad from .s2p?so many manufacturers are only giving the .s2p file.

Added after 2 hours 5 minutes:

Hi, now i have the schematic, please take a look!any suggestion?P.S. i'm going to use blf202 for the transistor
and also i keep getting this error saying that "Voltage source and/or inductor loop involving L-L4" Any idea?
Thanks a lot

4:1 rf transformer design

There is a mistake in the schematic. Both pins, 2 and 3 of M2 transistor are grounded.


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rf transformer schematics

Thanks, it's a mistake on my schematic because i drew it too quickly, but my board is connected properly(PIN 3 of M2 is not grounded)

Added after 4 minutes:

ok, this is my latest attempt, i use blf 202 and pin 3 of m2 is not grounded. the datasheet of the blf202 says that the VGS is ranging from 2.3-2.4v, so if i set the bias circuits to generate 2.3V each, and the input signal on each transistor is 2Vpp, shouldn't it work?but it doesn't on mine. Thanks

schematic transformer as amplifier

What do you mean with "not working"? Simulation errors as "inductor loop" are something different. They can be avoided by adding real world parameters as a small inductor series resistance. I also wonder about the purpose of using a small signal NF FET rather than a RF power FET in simulation.

voltage source and/or inductor loop involving

No, i'm doing real life experiment, not just simulation. The fet is replaced with BLF202, RF fet from NXP. What i mean not working is that all the signals are fine until it reached the input of each FETs(they were 2Vpp,50MHz, 180 deg out of phase) and i was hoping to get an 4Vpp,50MHz, and 200mA output...but the output is almost 0..let me upload the updated schematic

Added after 1 minutes:

P.S. by output i mean the output of the final transformer

jfet rf amplifier

It's hard to operate the amplifier with a that negative gain. As a first step, you should verify a suitable DC bias point. Then trace the RF level through the amplifier and check, if you didn't unintentionally invert one channel and effectively cancel the output signal.

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