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interpolation factor: 5
decimation factor: 2
channels: 6
input sample rate ( per channel) 260ksps
the data is arriving from an Avalon source stream which is being clocked at 25Mhz
(the ratio of data arrival over the Avalon channel to dead time works out to the net per channel data rate of 260k
this results in an output sample rate of 650ksps, the total bandwidth required is therefore 3.9msps for all six channels. I have derived the fir taps from matlab and set the LPF cutoff freq to be 33khz.
so I have a few questions which are not clear from reading the fir compiler manual or viewing the online tutorials.
1) can numbers less than one I.e.real values be entered in for sample rate? In this case 0.260?
2) does the sample rate entry apply to the input sample rate, the resultant output sample rate, or something else in the case of multichannel, multi rate filters?
3) will the fir work correctly if the ratio from clock frequency to sample rate is not an integer, I.e. Arbitrary real number greater than total aggregate sample rate. In this case 25mhz/1.3mhz = 19.23 or in the case of output rate 25mhz/(0.650*6)= 25mhz/3.9mhz= 6.41
thanks in advance.
richard
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1) You enter your fractional rate as integer interpolation of 5, and integer decimation of 2.
The actual fraction result is implied as 5/2 = 2.5 (what is 0.26 you mentioned?)
2) Normally the tool wants input rate.
3) yes, the ip will generate valid out signal to flag valid samples and non valid ones. You will enter clock rate somewhere.
your cut off of 33KHz may be too tight. You may be cutting off your own signal. You only need to cut off from edge of first image centred on 260*2 kHz or half of output Nyquist (650KHz) whichever is more restrictive. The filter works in the fast domain of 5 * 260 = 1300KHz
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