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Hello, I am using the V8 and I would like to get the specs from the lowpass filter in baseband?
I loaded the filter coefficients on the FDA tool to see the frequency response and using a FS of 50MHZ(based on your FPGA clock) the bandwidth is less than 8 MHZ. What's the cuttoff frequency.
Also at the receiver side there is subsytem for the ADC and filters, but no filter is implemented there.
Do you have any reason why the lowpass filter is not implemented at the receiver side in baseband?
thanks
Rafael
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In the reference design, the sampling frequency is 40MHz and the over-the-air bandwidth is 10MHz. There are two filters- one for 4x interpolation before the DAC and one for 1/4 decimation after the ADC.
The interpolation filter is implemented in the Tx subsystem in the OFDM model. This filter's coefficients are calculated in the OFDM Tx init script (it's the variable named 'interpFilter_4').
The decimation filter is implemented in the AGC core, since both the AGC and OFDM cores require access to post-decimation I/Q samples. This filter's coefficients are calculated with the MATLAB command fir1(31,1/4).
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Thank you very much for your support.
The fir at the receiver using fir1(31,1/4) is designed so that the cut-off frequency Wn must be between 0 < Wn < 1.0, with 1.0 corresponding to half the sample rate. In other words if FS=40MHZ , then the cuttoff would be 5 Mhz. In the freq response plot I can see that from 8 to 10 Mhz the attenuation factor is -60 db. do you have any reason why the cuttoff is at 5 Mhz?
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The filters have a pass bandwidth of 10MHz (+/-5MHz)
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