Polyphase FIR Filter¶
Block: Polyphase FIR Filter (frontend for a full PFB)
(
pfb_fir
)Block Author: Aaron Parsons
Document Author: Aaron Parsons
Contents |
Summary¶
This block, combined with an FFT, implements a Polyphase Filter Bank which uses longer windows of data to improve the shape of channels within a spectrum.
Mask Parameters¶
Parameter | Variable | Description |
---|---|---|
Size of PFB: (2?) | PFBSize | The number of channels in the PFB (this should also be the size of the FFT which follows). |
Total Number of Taps: | TotalTaps | The number of taps in the PFB FIR filter. Each tap uses 2 real multiplier cores and requires buffering the real and imaginary streams for 2PFBSize samples. |
Windowing Function | WindowType | Which windowing function to use (this allows trading passband ripple for steepness of rolloff, etc). |
Number of Simultaneous Inputs: (2?) | n_inputs | The number of parallel time samples which are presented to the FFT core each clock. The number of output ports are set to this same value. |
Make Biplex | MakeBiplex | Double up the inputs to match with a biplex FFT. |
Input Bit Width | BitWidthIn | The number of bits in each real and imaginary sample input to the PFB. |
Output Bit Width | BitWidthOut | The number of bits in each real and imaginary sample output from the PFB. This should match the bit width in the FFT that follows. |
Coefficient Bit Width | CoeffBitWidth | The number of bits in each coefficient. This is usually chosen to match the input bit width. |
Use Distributed Memory for Coefficients | CoeffDistMem | Store the FIR coefficients in distributed memory (if = 1). Otherwise, BRAMs are used to hold the coefficients. |
Add Latency | add_latency | Latency through adders in the FFT. |
Mult Latency | mult_latency | Latency through multipliers in the FFT. |
BRAM Latency | bram_latency | Latency through BRAM in the FFT. |
Quantization Behavior | quantization | Specifies the rounding behavior used at the end of each butterfly computation to return to the number of bits specified above. |
Bin Width Scaling (normal = 1) | fwidth | PFBs give enhanced control over the width of frequency channels. By adjusting this parameter, you can scale bins to be wider (for values > 1) or narrower (for values < 1). |
Ports¶
Port | Dir | Data Type | Description |
---|---|---|---|
sync | in | Boolean | Indicates the next clock cycle contains valid data |
pol_in | in | Inherited | The (complex) time-domain stream(s). |
sync_out | out | Boolean | Indicates that data out will be valid next clock cycle. |
pol_out | out | Inherited | The (complex) PFB FIR output, which is still a time-domain signal. |
Description¶
This block, combined with an FFT, implements a Polyphase Filter Bank which uses longer windows of data to improve the shape of channels within a spectrum.