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AH225 High Linearity PA - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement


SDO
 Post subject: AH225 High Linearity PA
Posted: Wed Dec 02, 2009 10:45 am 
 
Captain
 

Joined: Tue Aug 26, 2008 5:18 am
Posts: 22
Location: UK
Hello all,
Can anyone please advise me if AH225 will be suitable candidate for 400MHz (required bandwidth is 380-470MHz) application. Bias condtions are 5V@300mA.
main requirement is high IP3 ie. around 50dBm (out of balanced stage) using two tones each at 20dBm.
Data sheet shows application at 700MHz which I have scaled down to 400MHz in Microwave Office but this is only linear simulation and I am not sure about non-linear behaviour as there is no non-linear model for this device in Microwave Office.
Thanks in advance.
SDO


 
   
 
IR
 Post subject: Re: AH225 High Linearity PA
Posted: Fri Dec 04, 2009 5:10 pm 
 
Site Admin
 

Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
Hello SDO,

I see no problem with getting the IP3=+50dBm by using a balanced amplifier topology with the AH225. By using this topology, you will get an increase of 3dB in P1dB and IP3 (minus the insertion loss of the output hybrid coupler). IMD products will therefore be reduced by 9dB and the delta (P1-P3) will be around 6dB.

Pay attention to S11 matching, which seems to be difficult in the low frequency. Actually by using hybdid coupler it should be easier.

Another advantage of using the balanced amplifier for this device in this specific frequency of operation is that it will provide good stability. The AH225 has a very high gain in this frequency and it will easy oscilate when be used in single ended configuration.

Disadvantages are higher current and higher circuit costs.

Good luck!

_________________
Best regards,

- IR


 
   
 
SDO
 Post subject: Re: AH225 High Linearity PA
Posted: Mon Dec 07, 2009 12:58 pm 
 
Captain
 

Joined: Tue Aug 26, 2008 5:18 am
Posts: 22
Location: UK
Hello again,
Thanks for your reply. The problem I am facing is how to determine optimum load impedance for AH225 because all I have is sparameters given at a specific bias point. I have done linear simulation using Microwave wave office and produced my prototype based on that. It does show gain and return losses more or less same like simulation but IP3 is quite far away, single device is giving me around 41dBm with two tones each at 17dBm.
Is there anything I can do (apart from increasing bias voltage or current) or should I try to tune output match (a lengthy process) for better IP3?
Many thanks.


 
   
 
IR
 Post subject: Re: AH225 High Linearity PA
Posted: Mon Dec 07, 2009 1:58 pm 
 
Site Admin
 

Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
Hello,

Without non-linear model it is not possible to simulate.
Try asking the device's manufacturer for such a model.

From my experience, changing the bias will not bring much. For example, if you lower the device voltage you will only degrade the IP3. If you will reduce the current you will reduce the gain.

So the only significant thing is changing the output load. Try to find a direction which improves the IP3 and then follow it. Do it on a single device and not in the complete Balanced Amplifier structure.

_________________
Best regards,

- IR


 
   
 
SDO
 Post subject: Re: AH225 High Linearity PA
Posted: Tue Dec 08, 2009 1:24 pm 
 
Captain
 

Joined: Tue Aug 26, 2008 5:18 am
Posts: 22
Location: UK
OK thanks for your help. I'll try my luck by tunning output for better IP3. (as this is the only option left)

SDO






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