how to test the output of switch-cap filter

[nus_lin]

apparently, the testing probe will load the opamp and slow down the filter. what did you guys do to solve this problem. please recommend a solution.

 

[willyboy19]

There are at least two ways I am aware of to solve this issue:

1) Use a FET probe, which has only 1pF capacitive load on your SC amplifier output;

2) Add another wide band buffer with linearity much higher as your designed SC circuit. This may become very difficult if you already start with a high linearity SC circuit.

Thus, you may want to try 1). The FET probe is a little bit expensive, though.

 

[nus_lin]

There are at least two ways I am aware of to solve this issue:

1) Use a FET probe, which has only 1pF capacitive load on your SC amplifier output;

2) Add another wide band buffer with linearity much higher as your designed SC circuit. This may become very difficult if you already start with a high linearity SC circuit.

Thus, you may want to try 1). The FET probe is a little bit expensive, though.

thank willyboy. i am thinking of trying 2). the linearity is a concern, but not very stringent. do you have some topologies at hand? res-degenerated differential pair has large distortion.