Filter Performance Assessment Using Basic Equipment: A Practical Guide

[tim9000]

Hi,
Say I have a design for a filter, is there a method of bench-marking it's attenuation over a variety of loads and types of harmonics? (or even common and differential noises)

For instance, say I wanted to compare a filter to an LC filter or a π filter, how does one evaluate how much better or worse these are to each other and to other filters?

Cheers

 

[berkeman]

Hi,
Say I have a design for a filter, is there a method of bench-marking it's attenuation over a variety of loads and types of harmonics? (or even common and differential noises)

For instance, say I wanted to compare a filter to an LC filter or a π filter, how does one evaluate how much better or worse these are to each other and to other filters?

Cheers

In simulation, you would use one of the SPICE packages, preferably one that let's you use Monte Carlo variations to explore what happens over component tolerances.

For actual circuits, you can use a Spectrum Analyzer with Tracking Generator Output to scan the input signal to the filter and plot the output response (gain, not phase). Alternately, you can use the Gain-Phase measurement capability of an Impedance/Gain-Phase analyzer instrument like the HP 4194 (we have several in our Lab)...

http://www.testequipmentdepot.com/usedequipment/images/4194a.jpg

 

[tim9000]

In simulation, you would use one of the SPICE packages, preferably one that let's you use Monte Carlo variations to explore what happens over component tolerances.

For actual circuits, you can use a Spectrum Analyzer with Tracking Generator Output to scan the input signal to the filter and plot the output response (gain, not phase). Alternately, you can use the Gain-Phase measurement capability of an Impedance/Gain-Phase analyzer instrument like the HP 4194 (we have several in our Lab)...

http://www.testequipmentdepot.com/usedequipment/images/4194a.jpg
View attachment 195453

Thanks for the reply.
Also, is there any testing methodology for performing assessment with more basic equipment like a signal generator and an oscilloscope?
Cheers

 

[berkeman]

Thanks for the reply.
Also, is there any testing methodology for performing assessment with more basic equipment like a signal generator and an oscilloscope?
Cheers

Yes, you can certainly do basic testing with a signal generator and oscilloscope. You just end up using the cursors on the 'scope to make your amplitude and phase shift measurements, and putting them into a spreadsheet by hand for plotting. Display both the input and output waveforms on the display and make your measurements at frequencies of interest. I did that plenty back in my school days, before I had access to Gain-Phase instruments like the HP 4194.