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lmf100 switched capacitor questions

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The IC can work perfectly from a single 5v supply or a plus 2.5v and minus 2.5V supply if you connect its Lsh and Gnd pins correctly.
The notch frequency can be 1/50th or 1/100th of the clock frequency. The 60Hz notch example shows a resistor trick to get a variable frequency notch that is 1/000th the clock frequency that maybe limits the notch depth to only 40dB.
 
On page 24 of the datasheet they describe the notch filter shown in figure 23.
It says:
"This circuit yields a notch with about 40 dB of attenuation
at 60 Hz. A notch is formed by subtracting the bandpass
output of a mode 3 configuration from the input using the unused
side B opamp. The Q is 10 and the gain is 1 V/V in the
passband. However, fCLK/f0 = 1000 to allow for a wide input
spectrum. This means that for pin 12 tied to ground (100:1
mode), R4/R2 = 100. The offset voltage at the lowpass output
(LP) will be about 3V. However, this is an extreme case
and the resistor ratio is usually much smaller."
 
After messing with the circuit over and over I decided to move onto something different. It looks like the two ICs I have are damaged because now I get strange results. Regardless, the ICs are also expensive.

I want to experiment with a bainter notch however the circuit I built using a calculator has not worked but I may have some simple errors in connections. Have you heard of the bainter notch filter audio guru? Or anyone else?
 
The only notch filter I have ever made was using the LMF100 because I wanted the notch frequency to be controlled by the clock frequency that also set the frequency of my low distortion sinewave oscillator.
The Bainter oscillator is described in Google. It simply adds a highpass filter to a lowpass filter.
 
For my project I'd love to use the IC because of the clock feature as you have said but am just not having luck with it. I tried using two 9v together which gave me an output of about 6-7vrms from the 555. I tried a bunch of things but for all I know the lmf ICs were probly damaged from me not using it correctly or I may have got fake ICs, I do t know. May order a few more from a real vendor this time because I went to ebay for these lmf ICs.
 
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Oh and what did you do about the example resistor ratio when you built yours?
I can't find my schematic and I looked at my circuit board but it takes too much time to make a replacement schematic from it.
 
I am going to read the datasheet a lot better this time. I ordered two new ICs from mouser with fast shipping I'm going to try harder this time to get it right because sometimes I just throw things together and make mistakes.

Trying to get discreet filters perfect while worrying about q vs notch depth and perfect components is too tedious especially when I plan on making a dozen of these circuits. So, I will have to wait until about Wednesday to give it another shot.
 
The MAX7410 switched-capacitor notch filter IC is much easier to use than the older LMF100. Digikey has some available in through-hole packages in addition to surface-mount packages.
 
What is the notch depth with lmf100 ?

From the datasheet, the lmf100 notch example says it gives a depth of only -40db, however audio guru said it was due to a resistor ratio and that the IC should be capable of upto maybe 100db or so.

The more different methods I try the more impossible it seems to truly detect distortion to a good resolution for an ordinary person like myself anyway.
 
I made a sinewave oscillator with 10 over-sampled steps and filtered out its harmonics with two switched-capacitor Butterworth 4th-order lowpass filters. My LMF100 notch filter uses the same clock frequency as the lowpass filters and measures 0.005% distortion which is a notch depth of at least -86dB.
 
A result as good as even .01% would be satisfying to me... .005 is better but even .1% ain't half bad to me. Hopefully I can manage to get it to work.
 
I reciever an lmf90 in mail today. This IC is probly the simplest to use but after reading the datasheet better it looks like this IC can't produce much of a null...
 
Audioguru, I almost forgot to ask you, when you describe filtering an oscillating sinewave's harmonics out, are you referring to the clock or input signal? And why do so?

Oh and today I am redoing the lmf100 circuit. I am etching a small pcb for use as an adapter from soic 20 to normal through hole header pins to go in my breadboard.

I'm going to use a buck regulator and opamp to create a split rail 10v supply(+/-5v)

Hopefully all goes well.
 
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