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 RFEL : Models - DHBF
 
   

This page describes a fixed-point model for the RFEL range of Distributed Halfband Filter (DHBF) cores. The model is available for Matlab, uses fixed-point arithmetic throughout and has customisable bit-widths.

The model is designed to accurately represent the functionality of RFEL DHBF cores. It has been tested against RFEL's standard DHBF implementation and shown to be bit-true.

The model is designed to be fully parameterisable, to encompass the widest range of possible requirements. Many of the modelled configurations are provided by RFEL as optimised off-the-shelf FPGA cores; cores may also be tailor-made to meet higher specification requirements.

The Full Matlab Model Manual can be downloaded here

Features :

Parameter Matlab Model
Filter Length The filter must have 4K-1 taps, where K is any integer between 1 and 10000.The upper limit also depends on available memory.
Phase The initial phase of the filter and the LOs may be set to one of four values: 0, 1, 2 or 3. This parameter is fairly arbitrary since the final core is pipelined - it is provided only for equivalence to the hardware.
LO Frequency The DHBF filter may be used to downconvert signals from the first Nyquist region (in which case the LO is at fs/4) or the second Nyquist region
(in which case the LO is at -fs/4=3*fs/4).
Input Precision Customisable between 1 and 62 bits.
See note on 'Data Precision' below.
Tap precision Customisable between 1 and 62 bits.
See note on 'Data Precision' below.
Output Width Customisable between 1 and 62 bits.
See note on 'Data precision' below.
Output Scaling Customisable between 1 and 62 bits.
See note on 'Data precision' below.
Clipping The model provides the same clipping as the FPGA core in that when the filtered output signal overflows the output width, the signal saturates. An additional array is output to provide clip detection.
Processing type Block Processing
Block Input Size Any even integer
Block Output Size Half the input length.
Pipeline Delay
None
Data precision Up to 62 bits of fixed point precision is supported throughout. Intermediate sums and products must not exceed 62 bits precision.
Platforms Matlab for Windows. Tested on Windows 2000,
Matlab version 6.5.

Matlab Model

The DHBF model is implemented as a fully optimised MEX add-in for Matlab and can therefore be called from Matlab in the same way as any other function. Use of the model involves three stages, initialisation, processing and destruction.

Initialisation : The user specifies the model parameters (filter taps, phase, Nyquist region and all appropriate bit widths) and the function returns a handle. This handle is then used in all future processing.
Processing : The user supplies input data blocks to the model and retrieves the output of the halfband filter.
Destruction : The user calls clear on the model, which then deallocates all associated memory.