active filter design

Discussion in 'General Electronics Discussion' started by sarjan88, Apr 22, 2011.

1. sarjan88

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0
Apr 22, 2011
Design a circuit using op-amp that will reject the 60kHz power line noise and also reject high signal frequency above 800Khz. The stop-band width around the 60kHz centre frequency is 10kHz. Use a cascade of 1st order high pass and 1st order low pass filter to implement this circuit. The voltage gain at passband frequencies is 10.

As mentioned in the title, can sum1 tell me this should be a band reject or band pass filter?
i try to construct a band reject filter but the result seem like not correct.

here is my circuit using multisim

here is the result using AC analysis in decibel

can sum1 help me out of this?
thanks

Last edited: Apr 22, 2011
2. davennModerator

13,674
1,892
Sep 5, 2009
welcome to the forums

60kHz ? power line noise (freq) is 60Hz or 50Hz is some countries

cheers
Dave

3. sarjan88

3
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Apr 22, 2011
sorry..the image link is edited..based on the question provided to me it mention is 60khz.
the circuit i design based on formula i found in notes...i need to make a ac analysis and bode plot diagram...

4. duke37

5,364
769
Jan 9, 2011
I do not understand the question, however, It does say use the filters in cascode, I assume that this means in series. Your circuit has the two filters in parallel so that even if one filter rejects some signal, it will be supplied by the other filter. Try your 2 filters in series, adjusting the gain to suit. The final summing amplifier is then not needeed.

5. sarjan88

3
0
Apr 22, 2011
if i make it in series isnt it become a band pass filter??i thought this should be a band reject question, one of my friend told me that he think the question is want me to construct a avtive filter which reject 60khz frequency, then the center frequency is 60khz with bandwidth 10khz...so the filter should accept frequency from 0-55khz and 65khz to 800khz..and reject frequency from 55khz to 65khz
lecturer provide hint is "combine a lowpass and a highbass filter" and the question mention Use a cascade of 1st order high pass and 1st order low pass filter to implement this circuit