[SOLVED] Sallen key filter design,low pass

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HOW TO DESIGN SALLEN KEY LOW PASS FILTER FOR 10Hz WITHOUT INCREASE IN THE GRAPH OF FREQUENCY MAGNITUDE PLOT AFTER 5KHz.
I GOT GRAPH AS attached. HOW T O GET IT DECREASING THROUGHOUT OR ATLEAST DECREASING TILL 1MOhm.
 

This is a typical disadvantage of the S+K lowpass.
If necessary, choose another filter topology.
 

You can improve matters by picking your values better to minimize the higher op-amp output impedance effect at higher frequencies.
By making all capacitors 10 times smaller and the resistors 10 times larger, you get a much better response.
 

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  • SK_filter.gif
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These values seems to work okay.



The screenshot was snapped when the frequency was 11 Hz. As seen by the scope trace, the output has begun to diminish.

The sweep shows no abnormal activity above 5 kHz.
 

BradtheRad said:
.............
The sweep shows no abnormal activity above 5 kHz.
Click to expand...

No surprise. I think it`s hard to detect some signals in the time domain if they are 50...60 dB down.

- - - Updated - - -

E-design said:
You can improve matters by picking your values better to minimize the higher op-amp output impedance effect at higher frequencies.
By making all capacitors 10 times smaller and the resistors 10 times larger, you get a much better response.
Click to expand...

As an alternative and if you are allowed to use a second opamp, you can insert a unity-gain amplifier into the feedback network.
Then there is do signal entering the filter output through the feedback capacitor.
 

try using some other configuration like Multiple feedack filter!!
or else play with the values for better result increase or decrese values of resistor /capacitor by same ratio
 

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