Polyphase Real FIR Filter
==========================
| **Block:** Polyphase Real FIR Filter (``pfb_fir_real``)
| **Block Author**: Henry Chen
| **Document Author**: Ben Blackman

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| -  `Summary <#summary>`__                                                |
| -  `Mask Parameters <#mask-parameters>`__                                |
| -  `Ports <#ports>`__                                                    |
| -  `Description <#description>`__                                        |
|                                                                          |
|    -  `Usage <#usage>`__                                                 |
+--------------------------------------------------------------------------+

Summary 
--------
This block, combined with an FFT, implements a real 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\ :sup:`?` pnts)                | 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 2\ :sup:`*PFBSize*` samples.        |
+-----------------------------------------------+-----------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Windowing Function                            | WindowType      | Which windowing function to use (this allows trading passband ripple for steepness of rolloff, etc).                                                                          |
+-----------------------------------------------+-----------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Number of Simultaneous Inputs (2\ :sup:`?`)   | 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 Bitwidth                                | BitWidthIn      | The number of bits in each real and imaginary sample input to the PFB.                                                                                                        |
+-----------------------------------------------+-----------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Output Bitwidth                               | 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 Bitwidth                          | CoeffBitWidth   | The number of bits in each coefficient. This is usually chosen to match the input bit width.                                                                                  |
+-----------------------------------------------+-----------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Use Distributed Memory for Coeffs             | 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 (real) time-domain stream(s).                                 |
+-------------+-------+-------------+-------------------------------------------------------------------+
| sync\_out   | OUT   | Boolean     | Indicates that data out will be valid next clock cycle.           |
+-------------+-------+-------------+-------------------------------------------------------------------+
| pol\_out    | OUT   | Inherited   | The (real) PFB FIR output, which is still a time-domain signal.   |
+-------------+-------+-------------+-------------------------------------------------------------------+

Description 
------------
Usage 
^^^^^^
This block, combined with an FFT, implements a real Polyphase Filter
Bank which uses longer windows of data to improve the shape of channels
within a spectrum.