I am studying the designs of Second Order Butterworth high pass filter practically. enter image description here

The Capacitor values C1 and C2 described in standard textbooks are always in the range of picofarads.(e.g.,0.0047uF)

1.The input signal is Sin wave(Range of frequency- 10Hz to 1MHz) given by the Function Generator.

2.I use standard DSO to monitor input and output at Vin and Vout Terminals.

3.Op-amp used in the practical circuitry is 741.

If I design the value such that the capacitor value is 1uF(with designed resistance value as 530 ohms for Cutoff frequency fc=3Hhz)) then the Signal Input which was given by the function generator itself distorts.Why so?

Why is the input signal(at Vin) given from the function generator(Datasheet) should distort depending on capacitor values?

  • 2
    \$\begingroup\$ You have reduced the input impedance of the filter by a factor of 200. What impedance is it now? What load impedance is the generator able to drive? What voltage are you driving into that impedance? What current must the generator supply? What current is it rated to supply? \$\endgroup\$ – Brian Drummond Mar 16 '18 at 17:12
  • \$\begingroup\$ @BrianDrummond Attached datasheet of the function generator. \$\endgroup\$ – VKJ Mar 16 '18 at 17:23
  • \$\begingroup\$ @BrianDrummond I am driving around 1Vp-p sinwave as input from the genetor to the filter input \$\endgroup\$ – VKJ Mar 16 '18 at 17:26
  • \$\begingroup\$ For one thing, it's much easier to find tight-tolerance capacitors (with low temperature drift) for reasonable prices with values below about 10 nF. \$\endgroup\$ – The Photon Mar 16 '18 at 17:45
  • \$\begingroup\$ Do you have your function generator set in 600 ohm mode for output impedance? That device will be better in 50 ohm mode. \$\endgroup\$ – Andy aka Mar 16 '18 at 17:58

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