mri_filter_model.m

This is GMS down upper converter and down converter in simulink. you may understand the structure in

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%  $Id: mri_filter_model.m,v 1.1.2.3 2008/06/12 16:12:55 igork Exp $
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%  Purpose: This file function generate CIC and CFIR filters 
%  using MATLAB built-in filter generator
%-------------------------------------------------------------

%%

function [ hcic, hcfir] = mri_filter_model(...
    flarmor, fwidth, ...
    fclk, fs_cic,m_cic,...
    use_cfir,fs_cfir,m_cfir,...
    channel, ast, ShowPlots)

%% Filter design parameters
fpass = 1.2*fwidth;         % Upper frequency limit of MRI band
apass = 0.01;               % Passband ripple (dB)

%% Create CIC

ast_cic  = ast;             % Stopband attenuation of CIC first lobe
dd = 1;                     % Differential delay of CIC - 1 or 2
hcic = design(fdesign.decimator(m_cic,'cic',dd,fpass,ast_cic,fs_cic));
set(hcic, 'Arithmetic','fixed');
info(hcic)

if ShowPlots>=3
    fvtool(cascade(hcic,dfilt.scalar(1/(gain(hcic)))),'Fs',[fs_cic]);
    title(sprintf('CIC Magnitude Response (dB), R=%d',m_cic));
end

%% Create CIC compensator (CFIR)
% Determine the available taps using the selected number of MAC units
cfir_os = (fclk/fs_cfir)/channel;

% make sure that at least 32 taps are available, even if it means more than
% one DSP48 to be used
taps_cfir = max((cfir_os*2),64); 

% There is no need in more than 128 taps, even if there are available
% cycles.
taps_cfir = min(taps_cfir, 128);

n_cfir = taps_cfir-1;
macs = max(1,cfir_os/(2*taps_cfir));

display(sprintf('CFIR tap count is %d, using %d MACs',taps_cfir,macs));

% Set stop-band attenuation of Compensation FIR; 
ast_cfir = ast;  

for i=1:4

    % Allow built-in Matlab function to generate the CIC compensation response
    % Specification formats
    % fpass,fstop,apass,ast_cfir, ...              % Too loose, not tied to max order
    % 'n,fp,ap,ast',ord,fpass,apass,ast_cfir, ...  % Better for fixed order
    if m_cfir>1
        hcfir(i) = design( ...
            fdesign.decimator(m_cfir,'ciccomp', ...
            hcic.differentialdelay, ...
            hcic.numberofsections, ...
            'n,fp,ap,ast',floor(n_cfir),fpass,apass,ast_cfir, ...
            fs_cfir ));
    else
        hcfir(i) = design( ...
            fdesign.ciccomp( ...
            hcic.differentialdelay, ...
            hcic.numberofsections, ...
            'n,fp,ap,ast',n_cfir,fpass,apass,ast_cfir, ...
            fs_cfir ));
    end

    % Quantize filter coefficients
    set(hcfir(i),...
        'Arithmetic','fixed',...
        'CoeffWordLength',18,...
        'FilterInternals','SpecifyPrecision','RoundMode','floor');

    if ShowPlots>=3
        fvtool(hcfir(i),'Fs',[ fs_cfir ])
        title(sprintf('CFIR Magnitude Response (dB) with N=%d, Ast=%d',n_cfir,ast_cfir));
    end
    % Next loop adjustments
    ast_cfir=ast_cfir+10;
end



% Display the loop results in an overlay
if ShowPlots>=4
    fvtool(hcfir,'Fs',[ fs_cfir ],'ShowReference','off');
    title('Overlay of CFIR Magnitude Responses (dB)');
end

% Choose an option from the loop, cascade and analyze response (including
% passband zoom)
hcfir = hcfir(3);
if ShowPlots>=3
    fvtool(cascade(hcic,dfilt.scalar(1/(gain(hcic))),hcfir),'Fs',[ fs_cic ]);
    axis([0 1.5 -200 +10]);
    title('CFIR-CIC Cascaded Magnitude Response (dB)');
    fvtool(cascade(hcic,dfilt.scalar(1/(gain(hcic)))),...
           hcfir,...
           cascade(hcic,dfilt.scalar(1/(gain(hcic))),hcfir),...
           'Fs',[ fs_cic fs_cfir fs_cic ],...
           'Legend','off',...
           'ShowReference','off');
    axis([0 0.12 -0.8 +0.8]);   % Focus in on passband
    legend('CIC','CFIR','CIC-CFIR Cascade');
    title('Passband Zoom Overlay of CIC, CFIR and cascaded CIC-CFIR Magnitude Responses (dB)');
end

%% Filter cascade and overlay visualization
full_chain = cascade(hcic,dfilt.scalar(1/(gain(hcic))),hcfir);
if ShowPlots>=2
    fvtool(full_chain,'Fs',[fs_cic]); axis([0 2 -200 10]);
    title('Final Cascaded Magnitude Response (dB)')
    fvtool(cascade(hcic,dfilt.scalar(1/(gain(hcic)))),...
           hcfir,...
           full_chain,...
           'Fs',[fs_cic fs_cfir fs_cic],...
           'Legend','off',...
           'ShowReference','off');
    axis([0 2 -200 10]);
    legend off; legend('CIC','CFIR', 'Full Cascade');
    title('Final Overlaid Magnitude Responses (dB)')
end