I am busy with a high order low pass filter. How can I improve the response time of a filter? If I use a higher ordered filter, does it improve? Also, if I use an op amp with a faster slew rate, does it improve?
My application is that amplify and get filter the load cell signal. My load cell signal is changing between 1 Hz to 10 Hz.
There is three stages in my signal conditioning circuit. First stage Instrumentation Amplifier to amplify the signal(AD8221), second stage is second order low pass filter with OP07C op-amp (Sallen-Key type, corner frequency is 10 Hz), third stage is voltage follower with again OP07C.
According to my test results, when I compared original signal to output of amplifier (first stage) there was no significant delay between two signals. However when I compared original signal to output of voltage follower there was significant delay. The delay was approximately quarter of a period of original signal.
So I have thought that I have to improve my filter rise time. Or do I have to change my op-amp with higher slew rate one. According to all your answer, should I use higher cutoff frequecy with same op-amp (OP07C)?
Most of you mentioned "group delay" of a filter. What does "group delay" depend on? I got it firstly depends on corner frequency of a filter. Is there any effect order of filter to group delay?
Best Answer
You cannot greatly change response time of a low-pass filter by changing its' order. What you have to do is change its cutoff frequency - the higher the cutoff frequency, the faster the response.
Look at it this way. A low-pass filter removes high frequencies, right? And if you want the filter output to change more quickly it must contain more high-frequency components. You know, fast change means high frequency. So the only way to get faster response from the filter is to let more high-frequency signal through, and that means changing the cutoff frequency to a higher one.