Questions about switched cap filter

[sxb416]

I have some quention about swtiched cap filter.
1.what can i care about the amp design except SR, dc gain ,GBW?
2.I design a 2nd biiquad filter,
but the gain of the filter can't reach the 0db,I am sure the cap value is ok.
what can i do,advance the amp or change the cap value.
thank you

 

[LvW]

Re: about active filter

In short: Your circuit does not work as wanted.
But, do you really believe we can give you some help without knowing some details? (filter topology, S/C block realization, clock frequency, design bandwidth, opamp type...)

 

[sxb416]

Re: about active filter

The details is as follow :
1.The filter topology is in the figure, and the sample freq is 32K,

2.the opamp is full differentail ota,the type is the common 2nd ota add the resistor common mode feedback. the gain is 75db,the gbw is 1.8Meg,the SR is
4v/us.

 

[LvW]

Re: about active filter

The details is as follow :
1.The filter topology is in the figure, and the sample freq is 32K,

2.the opamp is full differentail ota,the type is the common 2nd ota add the resistor common mode feedback. the gain is 75db,the gbw is 1.8Meg,the SR is
4v/us.

The circuit shown (is it really necessary to compress the file?) is derived from "Filter solutions" and is based on opamps. Please note that an opamp is not an OTA ("the opamp is full differential ota").
But - how should we know if there was any error transferring the opamp into the ota topology? For example, what did you do with the last stage?

 

[sxb416]

Re: about active filter

Thanks for your reply,but I don't understand your mean.
First, the solution filter use the opamps for the filter.But the load of opa is a capcitance or huge resistor .why I need a opamp ( ota+buffer)?
Second,when I use a full differential ota simulate the filter,the pole and zero is right,and I only need to adjust the gain,but I use a single-end cascode amp ,I can't get the right waveform,wrong pole or zero is shown.
I am very puzzled.

 

[FvM]

about active filter

You are talking all the time about a circuit, you never showed!

 

[sxb416]

Re: about active filter

the figure is as follow.

 

[LvW]

Re: about active filter

...why I need a opamp ( ota+buffer)?
Who gave you the advice to use opamps ?

...,the pole and zero is right,and I only need to adjust the gain,
I can't get the right waveform,wrong pole or zero is shown.
Sounds contradictory.

I am very puzzled.
Me too.