FIR Filter
The Finite Impulse Response (FIR) filter shapes the incoming data and compensates for roll-off in the CIC filter. The I and Q FIR filters share the same set of coefficients. These coefficients must be symmetric. The FIR filters can be enabled/disabled by setting FIR Filter Enabled and CIC Filter Enabled properties.
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Note The FIR and the CIC Filters must have the same enable/disable setting. |
When using the FIR filter, consider the following:
Basic FIR Structure
The following figure shows a diagram of a typical N-tap FIR filter:
The structure of the FIR filter is a long shift register. Each tap in the shift register is multiplied by an associated coefficient (c(x) in the figure above). The results for all of the taps are then summed to create the final output of the filter.
Symmetric FIR filters
The FIR filters in the OSP block are symmetric. This means that the first and last taps have the same coefficient, the second and second to last taps have the same coefficient, and so on. Because the FIR filter in the OSP has an odd number of taps, the center tap does not have a matching tap.