about high order biquadical switched cap filter

[sxb416]

As we know,high order active sc filter need more than one 2 order biquadical switched cap filter to realize it.
The question is each 2 order filter is effect or not ?
I simulate the single 2 order filter, the Q and f0 is OK,
but if i add them together , the wareform is wrong.
why it is ?

 

[LvW]

As we know,high order active sc filter need more than one 2 order biquadical switched cap filter to realize it.
The question is each 2 order filter is effect or not ?
I simulate the single 2 order filter, the Q and f0 is OK,
but if i add them together , the wareform is wrong.
why it is ?

To answer your question you must supply with some more details:
* Amplifier: Opamp or OTA?
* Just for clarification: Two 2nd order Butterworth stages, for example, in series lead NOT to Butterworth 4th order.

 

[sxb416]

To answer your question you must supply with some more details:
* Amplifier: Opamp or OTA?
It is a full differential OTA.


* Just for clarification: Two 2nd order Butterworth stages, for example, in series lead NOT to Butterworth 4th order.

Thank you,you mean three 2nd order ellipic can realize a 3nd order bandpass filter(for example)? right?

 

[LvW]

Thank you,you mean three 2nd order ellipic can realize a 3nd order bandpass filter(for example)? right?

* What do you need? Lowpass or bandpass? Which transfer function response?
* Three 2nd order stages (lowpass or bandpass) result in a transfer function of 6th order! The order is determined by the maximum order of the denominator polynom.
(But I know that - unfortunately - some people and some design programs call a minimum order bandpass with a quadratic polynom "first" order.)