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how to design ic filter's tuning circuit?

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hsez

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Hello everyone,I'm designing a CMOS lowpass filter.Because the bandwidth of input signal is less than 2MHz,I choose the active RC filter type. A 4th order filter can be built by cascading two biquad blocks which every biquad contains two full differential OPA.I use capacitance array controlled by 4 bits digital signal to fullfill 5% precision.Now the problem is how to design a tuning block.Scarcely filter books tell about filter tuning.So despaired.Maybe they think filter should be on board not on chip. RC variation is an important thing in IC filters,It really bothers me.Can anyone recommend me some useful papers or give me some tips.Thanks a lot.
 

hsez

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vrs007,
both your papers are useful.The first is more interesting,while I'm thinking
of using cap array instead of resistor array.The second paper is some complicated and i'll read it more.
thank you very much.
 

vrs007

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The second one actually uses a cap bank and has a tuning logic
 

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