tomk
Newbie level 6
Hi,
I've got a circuit that consists of two identical low-pass multiple feedback filters in series, and I'm getting almost no attenuation through the second stage. The cutoff frequency is 1 KHz, and the signal that I'm putting through the filter has a component close to DC and a component at 25 KHz, which is what I'm trying to filter out. I get a lot of attenuation at 25 KHz through the first stage, but if I compare the signal out of the first stage with the signal after the second stage, they are almost identical.
Some other notes:
- The GBW product of the opamp is 7 MHz.
- If I replace the second stage with a simple RC with a cutoff of 1 KHz, the 25 KHz component is almost completely removed.
- I used **broken link removed** to choose part values for the discrete components.
Any thoughts on why I'm not getting any attenuation through the second stage would be a big help.
Thank you.
I've got a circuit that consists of two identical low-pass multiple feedback filters in series, and I'm getting almost no attenuation through the second stage. The cutoff frequency is 1 KHz, and the signal that I'm putting through the filter has a component close to DC and a component at 25 KHz, which is what I'm trying to filter out. I get a lot of attenuation at 25 KHz through the first stage, but if I compare the signal out of the first stage with the signal after the second stage, they are almost identical.
Some other notes:
- The GBW product of the opamp is 7 MHz.
- If I replace the second stage with a simple RC with a cutoff of 1 KHz, the 25 KHz component is almost completely removed.
- I used **broken link removed** to choose part values for the discrete components.
Any thoughts on why I'm not getting any attenuation through the second stage would be a big help.
Thank you.