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Drain current vs. Sweep output power - RF Cafe Forums

Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views. It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if you would like to post something on RF Cafe's Facebook page, please do.

Below are all of the forum threads, including all the responses to the original posts.

Post subject: Drain current vs. Sweep output power Posted: Mon Sep 19, 2005 5:06 am


Joined: Tue Mar 15, 2005 11:43 pm
Posts: 65
Location: Singapore
Hi all :

I have one question regarding drain current at sweep output power. I understand that at most cases, drain current will increase as output power increases. However, I encountered it is the other way round. The drain current decreasing as output power increases. Why is it so?

I'm sweeping the output power in lower region than saturation power.
and I'm sweeping dual-tone input power (for IM3 measurement).

Can anybody enlighten me?

Any advice is appreciated.

Thanks and Regards,


Post subject: RF Power SweepPosted: Mon Sep 19, 2005 11:50 am
The last time I saw something like that was at lower frequencies, but the amplifier needed neutralization - it was not very stable.

Hope this helps.

Good Luck!


Post subject: Posted: Mon Sep 19, 2005 8:27 pm


Joined: Tue Mar 15, 2005 11:43 pm
Posts: 65
Location: Singapore
Hi :

Thanks for your advice
By the way, the PA (3-stages) frequency range is 1.8GHz, and sweep Pout is from 17dBm to 27dBm, while the estimated P1dB >35dBm.

and the PA is unconditionally stable at this frequency range as K>1, |S11|<1 and |S22|<1.

So I'm not sure why the current decreasing when Pout increases?

Any advice is appreciated.

Thanks and Regards,


Post subject: Posted: Tue Sep 20, 2005 8:56 am
One possibility is that there is resistance on the bias lines. As the power increase, the current increases, droping more voltage therefore turning the amplifier down. Check the voltage at the input of th amplifier to make sure that the bias voltage you think is there actually is.

Posted  11/12/2012
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