# vrf complex to string

Question asked by VRFuser on Mar 12, 2008
VGA? Variable gain amplifier?

I'm not sure there is any interpolation method other than linear that guarantees that the result passes through the data points.

Are you sure the curve must pass through the data points? That seems like an arbitrary requirement. So what if it doesn't as long as you meet spec?

If the above is a real requirement, then are you sure you can't use linear interpolation?

I've written a lot of software for VVA (voltage variable attenuator) characterization and use a linear interpolation to fill in the points between measurements. It works quite well. I do adjust the number of data points depending where I am in the curve.

We have one product that is controllable over a 50dB range in 0.25dB steps. I characterize it in 1dB steps in its linear range and 0.5dB steps in the non-linear regions, then linear interpolate the result into a data set that covers the whole range in 0.25dB steps. The technique saves time and yields good data.

-Bill

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From: David Watling [mailto:watling@IceraSemi.com]
Sent: Wednesday, March 12, 2008 5:29 AM
To: VRF
Subject: [vrf] Bezier curves

Hi all,

I am measuring a VGA by setting a DAC value, and measuring RF power.

I want to reduce the number of measurements I take by using curve smoothing (non-linear interpolation).  The important thing is that the curve MUST pass through the measurement points.  This means that regression is not the answer.  I have tried ‘cubic spline’ (Matlab ‘spline’), but it does odd things at the ends.  I wondered if Bezier curves would be appropriate, and if so, has anyone got a Bezier function I could make use of?

Best Regards

David Watling

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