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PD55025 power amplifier

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shanthi rao

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We are using PD55025 25W Power Amplifier for 30-88MHz.we want to achieve power of 10W.we are facing problem in matching the circuit to 30-80MHz.please suggest.

Regards,
Shanthi.
 

You mean wideband matching to 50 ohm load? A usual solution is by transmission line transformers.
 
shanthi rao said:
We are using PD55025 25W Power Amplifier for 30-88MHz.we want to achieve power of 10W.we are facing problem in matching the circuit to 30-80MHz.please suggest.

Regards,
Shanthi.
Click to expand...

Very tricky at such low frequencies but you can use co-axial line transformers with ferrite beads. Only these provide high impedance transforming ratios. Look for applications notes from Freescale or NXP (Ampleon).
 
yes..i have tuned it with line transformers.the input return loss through out the band is around 4dB.please suggest for better return loss.
 

I see that the datasheet has no detailed impedance data for the 30 to 88 MHz range. So you need to measure it for the intended power point to design the matching network. Or are you reproducing an existing design for PD55025?

I presume you know that a small signal measurement, e.g. with a standard network analyzer isn't suitable. How did you determine the 4 dB return loss? With a power generator and directional coupler?
 

According to the S parameters provided in the datasheet, the gain of PD55025 at 50 MHz is about 23dB (for all bias options). Perhaps the gain is even higher at 30 MHz (no information at this frequency).
This relative high gain would make the wideband PA design to be a challenge.
I would recommend to use two PD55015-E (15W each) in push-pull configuration, which will give better wideband performances than a single transistor.
You can find on the net a lot of examples how to make the wideband transformers for a push-pull configuration.
https://www.farnell.com/datasheets/1854812.pdf
 

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