FIR filter in Matlab for bandpass 250kHz - 700kHz and sampling frequency 250MSPS

[umaair_653]

Hi all,
I want to design filter to implement on FPGA with a mentioned parameters in subject but when i am starting to design it on matlab fdatool, it gives very high order filter result, and when i decrease or set by myself upto 10 order its impulse response is not good as i want.
Any idea will be highly appreciable.
Regards,
Umair

 

[FvM]

You give the explanation in the question title. The minimal FIR filter order is related to the fs/fc ratio. With this sampling frequency, you can't make even a poor FIR filter with less than e.g. 500 or 1000 taps.

Possible solutions:
- design a multirate filter with decimation before the final filter
- design an IIR filter. It must have increased accumulator resolution (e.g. 10 extra bits) to handle the fs/fc range without dynamic loss.

 

[umaair_653]

Thanks for your reply, but what did on on fdatool is to shift filter level (fc) towards high frequency like 5MHz and it give magnitude response about -9dB on 300kHz but with high order and high pass filter.
it will be right ?? means for example in case of high pass filter officially i want to implement filter with same sampling rate, fc = 300kHz but i will take coeficients with fc = 5MHz or 3 MHz it will work fine??
apparently it will work. . .