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FW: vrf Bezier curves - minor improvement

Question asked by VRFuser on Mar 12, 2008
That's very cool. It might be an improvement to my linear technique. I'm going to try it on my own data to see how it looks. Thanks for posting...
 
 


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From: David Watling [mailto:watling@IceraSemi.com]
Sent: Wednesday, March 12, 2008 2:23 PM
To: VRF
Subject: FW: [vrf] Bezier curves - minor improvement



Minor improvement

 


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From: David Watling
Sent: 12 March 2008 18:10
To: VRF
Subject: RE: [vrf] Bezier curves

 

Hi Guys,

Thank you for your input.  I ended up on Wikipedia and other web pages, and making rather heavy use of one of our mathematicians (poor guy).

Here is my solution attached.  Seems to work fine.

 

Regards

 

Dave Watling

 


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From: Williams, Dan [mailto:Dan.Williams@analog.com]
Sent: 12 March 2008 17:25
To: VRF
Subject: RE: [vrf] Bezier curves

 

Not sure if this is along the lines of what you want but there is an Excel bit here that demonstrates how the Excel smoothing function works. I was trying to get this into a useable VEE form but got pulled off to other tasks before I finished it. Maybe close to what you are looking for.

 

http://www.xlrotor.com/resources/files.shtml

 

Look for the bit that says;

Smooth_curve_bezier_example_file.xls

 

Dan

 


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From: David Watling [mailto:watling@IceraSemi.com]
Sent: Wednesday, March 12, 2008 12:47 PM
To: VRF
Subject: RE: [vrf] Bezier curves

Hi,

Correct: VGA = variable gain amplifier.

Linear interpolation creates sudden changes in slope, which reduces the quality of our radio.  I’m struggling to remove these discontinuities.  I’m having some limited joy with Wikipedia on Bezier curves, but I still get some discontinuities.

 

Dave

 


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From: William.Drago@L-3com.com [mailto:William.Drago@L-3com.com]
Sent: 12 March 2008 16:05
To: David Watling; VRF
Subject: RE: [vrf] Bezier curves

 

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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