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AH225 High Linearity PA - RF Cafe Forums
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SDO
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Post subject: AH225 High Linearity PA
Posted: Wed Dec 02, 2009 10:45 am
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Joined: Tue Aug 26, 2008
5:18 am Posts: 22 Location: UK
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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
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IR |
Post subject: Re: AH225 High Linearity PA
Posted: Fri Dec 04, 2009 5:10 pm
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Joined: Mon Jun 27, 2005
2:02 pm Posts: 373 Location: Germany
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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
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SDO |
Post subject: Re: AH225 High Linearity PA
Posted: Mon Dec 07, 2009 12:58 pm
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Joined: Tue Aug 26, 2008
5:18 am Posts: 22 Location: UK
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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.
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IR |
Post subject: Re: AH225 High Linearity PA
Posted: Mon Dec 07, 2009 1:58 pm
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Joined: Mon Jun 27, 2005
2:02 pm Posts: 373 Location: Germany
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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
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SDO |
Post subject: Re: AH225 High Linearity PA
Posted: Tue Dec 08, 2009 1:24 pm
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Joined: Tue Aug 26, 2008
5:18 am Posts: 22 Location: UK
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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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Posted 11/12/2012
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