Electronics > Beginners

Can you use an active LP filter with gain=1 as a buffer also?

(1/2) > >>

I guess the question really boils down to whether an active filter circuit has a low output impedance. In my design I am using an opamp to create a low pass filter with a gain of 1. Can I also use this as the buffer amp, or do I need another opamp after it to specifically be used as a buffer? There doesn't appear to be an easy answer on Google.

Thanks in advance

The usual active fitlers (Sallen-Key and multiple feedback) have a low output impedance, however that are also others that need an extra buffer. If directly from an OPs ouput there is usually no need for an extra buffer.

Excellent. Thanks for the prompt reply.

Note that the input impedance matters as well, so you may need a buffer there instead.


This is important point about input impedance as "seen" from the filter input, often overlooked and one cause (there are many) of performance deviations from ideal. The SK types have a very complex and frequency dependent input impedance over the intended frequency range.  To reduce the effect of the input impedance, the driving source impedance needs to be low relative to the input impedance over the frequency range.



[0] Message Index

[#] Next page

There was an error while thanking
Go to full version