Polyphase FIR Filter

Block: Polyphase FIR Filter (frontend for a full PFB)
(pfb_fir)
Block Author: Aaron Parsons
Document Author: Aaron Parsons

Contents

Summary
Mask Parameters
Ports
Description

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 2^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^?)	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.