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Drain current vs. Sweep output power - RF Cafe Forums

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Jeanalmira

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

General

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,

Jean

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Guest

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!

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Jeanalmira

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

General

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,

Jean

Top

Guest

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.

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