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jayce3390
Joined: 22 May 2007
Posts: 84
Helped: 2
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 07 Jul 2008 14:30 Resistor for high power amplifier design |
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Hi,
I am designing a 30W Rf hybrid microstrip power amplifier in S frequency band.
I encounter stability problem that's why I need to implement serie resistor on the RF path to improve the power amplifier stability.
I am looking for a 10-20 ohms chip resistor able to support 1 to 4W power handling range.
Can somebody give me manufacturers names?
Thank you very much.
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khouly
Joined: 20 Oct 2003
Posts: 2455
Helped: 340
Location: EGYPT
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| 07 Jul 2008 15:01 Resistor for high power amplifier design |
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this resistor will decrease the gain of ur amplifier.
for resistor manufacturers check uniohm.
i think u need to check the matching for stability
Khouly
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jayce3390
Joined: 22 May 2007
Posts: 84
Helped: 2
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| 07 Jul 2008 16:12 Re: Resistor for high power amplifier design |
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Thank you for your answer.
Yes of course the resistor makes the gain & PAE worse but unfortunately I have to add this resistor in the matching network to make the Rollet stability factor upper than 1.
I tried to modify my input matching network in order to improve the global stability but I don't find solution.
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khouly
Joined: 20 Oct 2003
Posts: 2455
Helped: 340
Location: EGYPT
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| 07 Jul 2008 16:33 Resistor for high power amplifier design |
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u need to study the source of instabilty , u need to plot load and source stability circiles and check which one can be modfied ,
even u can mismatch the load to get ur amplifier stable
khouly
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VSWR
Joined: 07 Feb 2002
Posts: 630
Helped: 53
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| 07 Jul 2008 17:38 Re: Resistor for high power amplifier design |
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It's a waste of power to add this resistor in the RF path to make the amplifier stable. In many cases there may be another solution. WinRAR and upload your project/simulation files here so we can take a look.
| Quote: |
I encounter stability problem that's why I need to implement serie resistor on the RF path to improve the power amplifier stability.
I am looking for a 10-20 ohms chip resistor able to support 1 to 4W power handling range.
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khouly
Joined: 20 Oct 2003
Posts: 2455
Helped: 340
Location: EGYPT
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| 07 Jul 2008 18:02 Resistor for high power amplifier design |
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i agree with VSWR
Khouly
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RF-OM
Joined: 03 Aug 2007
Posts: 607
Helped: 113
Location: The Earth
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| 07 Jul 2008 22:11 Re: Resistor for high power amplifier design |
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| I agree with VSWR. Usually this resistor is below 5 Ohm. Do you have S-parameter file for your transistor?
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jayce3390
Joined: 22 May 2007
Posts: 84
Helped: 2
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| 08 Jul 2008 11:27 Re: Resistor for high power amplifier design |
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RF-OM,
Yes I have S parameters files of my transistor from 0.5 GHz to 10GHz.
You can find it in attachment.
VSWR & Khouly, I will upload my project as soon as possible.
thank you very much
Last edited by jayce3390 on 23 Jul 2008 11:16; edited 2 times in total |
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biff44
Joined: 24 Dec 2004
Posts: 1258
Helped: 160
Location: New England, USA
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| 08 Jul 2008 12:02 Resistor for high power amplifier design |
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| http://www.usmicrowaves.com/res/power_beo/custom_beo_microwave_power_chip_resistors.htm
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RF-OM
Joined: 03 Aug 2007
Posts: 607
Helped: 113
Location: The Earth
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| 09 Jul 2008 18:34 Re: Resistor for high power amplifier design |
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| I am on the business trip now. When return back to home I will check stability analysis for you.
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RF-OM
Joined: 03 Aug 2007
Posts: 607
Helped: 113
Location: The Earth
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| 12 Jul 2008 0:09 Re: Resistor for high power amplifier design |
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I check your S2P file today for stability analysis with LINC2 circle utilities. It looks like your amplifier should be stable in 2-4 GHz range (S-band), but be unstable on higher frequencies closer to 10 GHz. Please see attached jpg file with this simulation. May be you can use filter to limit the bandwidth?
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jayce3390
Joined: 22 May 2007
Posts: 84
Helped: 2
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| 15 Jul 2008 9:46 Re: Resistor for high power amplifier design |
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Hi,
Thank you for your help RF-OM, My device seems to be stable at 2 GHz, but We can't be sure that it will be stable at 2.1GHz for example?
I thought that the the device should be stable at all frequencies, not only in the frequency band... is it true?
thx
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RF-OM
Joined: 03 Aug 2007
Posts: 607
Helped: 113
Location: The Earth
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| 15 Jul 2008 21:56 Re: Resistor for high power amplifier design |
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| Of course it is true. But often you may artificially cut off the bandwidth in order to eliminate unstable region and make your circuit stable. There are different ways to do it. For example stabs at the input or output, some kind of filtering and so on. If your transistor is unstable and you do not want to change the bandwidth or cannot do this, you need to chose another transistor.
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BigBoss
Joined: 17 Nov 2001
Posts: 907
Helped: 44
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| 16 Jul 2008 1:05 Resistor for high power amplifier design |
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Frequency selective negative feedback will improve the overall stability.Adding an extra pole with RC or RL circuits on the frequency where the stability decreases, this will help you to pull up the stability factor more than one..
Note that, the stability circles tell me that amplifier is NOT unconditionally stable..
Take care. !!
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RF-OM
Joined: 03 Aug 2007
Posts: 607
Helped: 113
Location: The Earth
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| 16 Jul 2008 5:42 Re: Resistor for high power amplifier design |
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| It is absolutely right. I checked stability circles and analysis clearly shows the problems. But without knowing all design details it is hard to give exact recommendations. There is not one frequency problem, it is rather relatively broadband and frequencies are high enough to make it complicated to use lamp elements. RC circuits will almost for sure make things worse due to parasitics. I think that there must be solution that limits the bandwidth for at least 5 or 6 GHz, definitely not more (if I remember the stability analysis right). Layout may also contribute a lot, especially parasitic inductance in emitter or source connection. Without seeing the design it is hard to make right conclusion. Probably these details were included in file provided by the author of the question, but I was not able to open it and check.
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jayce3390
Joined: 22 May 2007
Posts: 84
Helped: 2
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| 16 Jul 2008 10:31 Re: Resistor for high power amplifier design |
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This is not a wideband application, only 1,8% around ~2 GHz, I added a serie resistor to the RF path of the input matching network that improved the Rollet stability factor but makes the PAE decreasing by 10 pts. 
I think it is not a good idea to add resistive element at the output matching in terms of PAE, I think it is worse.
Is it possible to use shunt resistor instead of series ?
BigBoss you advise me to use a circuit between the output and the input pads of my device, RC series for example?
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jayce3390
Joined: 22 May 2007
Posts: 84
Helped: 2
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| 22 Jul 2008 10:44 Re: Resistor for high power amplifier design |
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I can't find the source of unstability in my design. The used device shows K factor <1 full analysis band.
Is it possible to design with this device?
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