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[SOLVED] Low Pass Filter Design using only mosfets

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Newbie level 3
Dec 29, 2012
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Hey guys,

I need to design a low pass filter using only mosfets, i am not allowed to use any op-amps. All I need is a basic circuit schematic for low pass filter using only mosfets. Thank you, please help.

PS. I searched the forum but nobody has asked a simple question like mine, all the filter related topics are complex than my problem :).

The question isn't really clear. I tend to understand active filters with MOSFET amplifiers.

That's basically possible. I can imagine e.g. Sallen-Key filters with MOSFET source followers as buffer. To turn the post in a meaningful question, you would want to mention a filter specification.

Needless to say that you can also design passive filters without any semiconductor components.
Yeah, question is to design an active low pass filter with MOSFET amplifiers. To be specific my filter must have

-Cutoff Frequency at 900khz
-Gain must be 20dB or higher
-The design could only have MOSFETs or BJTs, (i.e. I can use CA4056 array but not UA741 Op-Amp.)

Sorry for not being clear before.

Still not a complete specification.

Particularly I don't see what the gain specification has to do with the low-pass filter itself. It just says there should be an additional amplifier stage, e.g. in common source configuration.
Thank you crutschow and FvM for your help. I am an engineer student who is just taking the Analog Electronics Course for the first time because of that I had problems explaining my situation. Anyway thanks :)

Hi tailsmp,

attached you will find a second order lowpass in Sallen-Key topology using two BJT´s. Perhaps it helps to find a solution for your problem.
I do not have any parts values - perhaps circuit simulation can help to find suitable values.


  • BJT_Filter.pdf
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