Doubt regarding digital filter.

Hi all

I have a doubt regarding digital filter.

If the input signal is of bandwidth 20KHz and if it is sampled at a rate of 320ksps.The bandwidth of
the digital filter is 0- 20 KHz.
Now my doubt is , when the sampled signal is passed through the digital filter then, will the input signal will get passed through it or it will get rejected as it is sampled at a rate of 320ksps

Kindly reply, it's very urgent.

Thanks a lot in advance.

Heya Amit,

The signal will make it through the filter OK, since it is specified to pass signals 0-20 kHz. The 320 ksps sampling rate is just an implementation detail of the filter. You could just as well have your desired 20 kHz bandwidth signal represented within a 5 GSps data stream and although the filter would necessarily be _longer_ (an implementation detail) it could be designed to have exactly the same response as your 320 ksps system.

Thanks Thylacine.

So, does this mean that the digital filter only concern about the signal frequency and will not bother about the sampling frequency ( or sampling rate) ?

Absolutely. The sampling frequency will affect the implementation of the filter (how many multiply-accumulation operations are required for a given response, for example) but it's frequency response dictates 'what it does' (e.g. passes, attenuates, phase shifts etc) to the input samples.

Be aware though, that these two 'attributes' of a filter (sampling rate and response) aren't independent. i.e. if you design a filter to have a certain frequency response at a given sampling rate, its' response will change as the sample rate is varied (generally scaling in linear proportion). There is more written than can be imagined (!) about digital filters so I'm not sure where would be the best place to point you for further reading, other than good ol' Wikipedia: Digital filter - Wikipedia, the free encyclopedia.

Good luck!