Is there any advantage in connecting up high pass filter first and then low pass filter to achieve a simple band pass filter. Or the other way around is better? Will there be any change based on the order of connection of filters?
Electrical – Does the order of connecting the low pass and high pass filter make any difference
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Related Solutions
From wiki, the transfer function polynomials for several Bessel filters are: -
If you took two 2nd order filters and multiplied the polynomials you do not end up with the polynomial of a 4th order Bessel filter. You end up with this: -
\$s^4 + 6s^3 + 15s^2 + 18s + 9\$
This informs you that cascading two independent 2nd order Bessel filters does not produce a 4th order Bessel filter or, in other words you have to calculate the values of the components in both 2nd order filters taking into account that you are trying to implement a 4th order system. You might get lucky of course but if you just cascade 2 2nd order Bessel filters it won't be a 4th order Bessel filter.
It's not just Bessel filters that this rule applies to.
Here's a website that might help. The calculator appears to keep a common value for the capacitors used but there are 6 resistors all having different values: -
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.
Related Topic
- Electronic – Why does the Sallen-Key 2nd Order High-Pass filter return a square wave? (Beginner question)
- Electronic – Does Q-Factor matter for low pass and high pass filters
- Electrical – Difference between using a first order low pass filter and a second order
- Electronic – Sallen-Key low pass filter cutoff frequency
Best Answer
One thing to worry about when cascading filters is loading. It's possible that when this is taken in to consideration, the component values will be nicer for one configuration.