Pipelined FFT Models

A set of fixed-point models with customisable bit-widths for the RFEL range of pipelined FFT cores, are available for Matlab software tools.

The models are designed to accurately represent the functionality of RFEL pipelined FFT cores. They have been tested against RFEL's standard pipelined FFT implementation and are bit-true provided that the modelled bit-widths are correctly set to avoid overflow.

The models are designed to be fully parameterisable, so as to encompass the widest possible range of 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 Radix 2 Matlab Model Manual can be downloaded here

Features :

Parameter	Matlab Model
FFT size	Powers of 2 from 2 to 32M. The upper limit also depends on available memory. Note: For the evaluation copy of the software, the range of FFT sizes will be restricted. A full installation of the model provides FFTs with fully parameterisable sizes.
Oversampling rate	The model is not limited to critical sampling at the output. The output oversampling rate is specified in terms of the decimation through the model (see below).
Decimation	Integers from 1 to the FFT size. Setting the decimation equal to the FFT size provides a critically sampled output; setting decimation to half the FFT size yields a twice oversampled output, and so on.
Bin ordering	Either unshifted: from [0, 1, 2, ..., K-1] or shifted: [K/2, K/2+1, ..., K-2, K-1, 0, 1, 2, ..., K/2-1]
FFT precision	Fully customisable at input and output and at all intermediate stages between 1 and 62 bits. See 'Data precision' below.
Twiddle precision	Customisable between 1 and 62 bits. See 'Data precision' below.
Processing type	Block processing
Block input size	Equal to the decimation parameter set at initialisation
Block output size	Equal to the FFT Length
Output Rate	n/a
Pipeline delay	None
FFT Type	Radix-2 Decimation In Frequency.
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.

Use in the Matlab Environment

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

Initialisation :	The user specifies the model parameters (FFT size, Decimation factor, Bin ordering and all appropriate bit widths) and the function returns a handle. This handle is then used in all future processing.
Processing :	The user streams data into the model and retrieves the output of the FFT.
Destruction :	The user calls clear on the model, which then deallocates all associated memory.