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Simulators >> RF Simulators >> Input power extrapolation point
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Message started by ssk_288 on Jul 28^th, 2005, 2:40am

Title: Input power extrapolation point
Post by ssk_288 on Jul 28^th, 2005, 2:40am

Hi all

I am a new user to Cadence. I am simulating a downconversion mixer in SpectreRF. I am using PAC analysis with PSS.

To plot the IP3 it asks to specify "input power extrapolation point" .

1) What does that mean?

2) As I change its value the IP3 also changes?

Thanking you in advance

regards
SUDHIR S. KUDVA

Title: Re: Input power extrapolation point
Post by sheldon on Jul 28^th, 2005, 5:32am

Sudhir,

1) The IP3 is figure of merit extrapolated from the
"linear" region of operation. Since the IP3 exists
outside the "linear" region, it is calculated by
extrapolation.

By "linear" we are refering the region where the
output power increases linearly as the input power
increases.

You might want to make sure that you are at least
>10dB below the 1dB compression to make improve
quality of the extrapolation.

2) As long as the circuit is behaving linearly, the IP3
point should the same. When the output starts to
compress, the extrapolation is no longer valid.

The other factor to be aware of is that the
accuracy of the third harmonic calculation is the
lower limit of the extrapolation accuracy.

You should check that the slope of the third-order
intermodulation product 60dB/decade. If the slope
is less than accuracy of the simulation should be
improved.

BTW, there should be an app-note on simulating
mixers on Sourcelink that should explain IP3 with
pictures. Also the SpectreRF theory manual may
provide useful information.

Best Regards,

Sheldon