gsm_duc_cic_filters.m

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

function [ hcic, hcfir, hpfir ] = gsm_duc_cic_filters(...
    fclk,n_ch,...
    fs_cic,m_cic,...
    use_cfir,fs_cfir,m_cfir,...
    use_pfir,fs_pfir,m_pfir,...
    ShowPlots)


%% Filter design parameters
fpass = 80e3;               % Upper frequency limit of GSM band of interest
fstop = 100e3;              % Transition point of GSM mask
apass = 0.01;               % Passband ripple (dB)
scale_tweak = [ 1.0 1.1 ];  % PFIR and CFIR coefficient scaling factors

%% Create CIC
ast_cic = 120;              % Stopband attenuation of CIC first lobe
dd = 1;                     % Differential delay of CIC - 1 or 2
hcic = design(fdesign.interpolator(m_cic,'cic',dd,fpass,ast_cic,fs_cic));
set(hcic, 'Arithmetic','fixed','InputWordLength',18,'InputFracLength',17);
info(hcic)
if ShowPlots>=3
    fvtool(cascade(hcic,dfilt.scalar(1/(gain(hcic)*m_cic))),'Fs',[fs_cic]);
    axis([0 10 -200 10]);
    title(sprintf('CIC Magnitude Response (dB), R=%d, gain=%d',m_cic,gain(hcic)));
end

%% Create CIC compensator (CFIR)
cfir_use_firceqrip = 1;   % Specify method, firceqrip or Matlab CIC comp
%k_cfir = 0.912;          % Scaling factor for CFIR, to prevent overflows
                          % due to additional passband gain

for macs=2:-1:1
    % Determine the available taps using the selected number of MAC units
    cfir_os = fclk/fs_cfir/n_ch;
    taps_cfir = (macs*cfir_os*4-1);
    n_cfir = taps_cfir-1;
    display(sprintf('CFIR tap count is %d, using %d MACs',taps_cfir,macs));
    if n_cfir <15
        error(sprintf('CFIR tap count of %d is too low, using %d MAC units!',taps_cfir,macs));
    end
    
    % Set stop-band attenuation of Compensation FIR; if using firceqrip with a
    % slope, start with a low basic stop-band attentuation, else go for higher
    % stop-band
    if cfir_use_firceqrip == 1
        ast_cfir = 50;
    else
        ast_cfir = 85;   % Stopband attenuation of Compensation FIR
    end
    
    for i=1:4
        if use_cfir == 1
            if cfir_use_firceqrip==1
                % Use fircerip method of CFIR generation using a fixed
                % filter order, determined by the FIR hardware capabilities
                w = 0.5;        % Sinc frequency factor

                ripple = 10^(apass/20);         % Maximum value of ripple
                err_pass = (ripple-1)/2;        % Ripple error
                ast    = 10^(-1*ast_cfir/20);   % Convert stop-band attenuation to weight
                slope  = 80;                    % Slope in stop-band, db/rad/sample
                wpass  = fpass/(fs_cfir/2);     % Normalized frequency pass-band edge

                cfir = firceqrip(...
                    n_cfir,wpass,[err_pass, ast],'passedge',...
                    'slope',slope,...
                    'invsinc',[w,hcic.numberofsections]);
                
                %cfir_gain(i) = m_cfir*scale_tweak(2);
                %cfir_scaled = cfir*cfir_gain(i);
                [ cfir_scaled cfir_gain(i) ] = scale_coeffs(cfir,m_cfir);
                cfir_scaled = cfir_scaled*scale_tweak(2);
                cfir_gain(i) = cfir_gain(i)*scale_tweak(2);
                
                if m_cfir>1
                    %hcfir(i) = mfilt.firinterp(m_cfir,cfir*m_cfir);
                    hcfir(i) = mfilt.firinterp(m_cfir,cfir_scaled);
                    %hcfir(i).Numerator
                else
                    hcfir(i) = dfilt.dffir(cfir);
                    %hcfir(i).Numerator
                end
            else
                % 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.interpolator(m_cfir,'ciccomp', ...
                        hcic.differentialdelay, ...
                        hcic.numberofsections, ...
                        'n,fp,ap,ast',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
                cfir_gain(i) = scale_tweak(2)*m_cfir;
                hcfir(i).Numerator = hcfir(i).Numerator*scale_tweak(2);
            end

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

            if ShowPlots>=4
                fvtool(cascade(hcfir(i),dfilt.scalar(1/cfir_gain(i))),'Fs',[ fs_cfir ])
                title(sprintf('CFIR Magnitude Response (dB) with N=%d, Ast=%d, firceqrip=%d',n_cfir,ast_cfir,cfir_use_firceqrip));
            end
            % Next loop adjustments
            ast_cfir=ast_cfir+10;
        else
            % Bypass PFIR
            hcfir(i) = dfilt.scalar(1);
        end
    end
end

% Display the loop results in an overlay
if ShowPlots>=4 && use_cfir==1
    % fvtool(hcfir,'Fs',[ fs_cfir ]);
    for i=1:4
        htemp(i)=cascade(hcfir(i),dfilt.scalar(1/cfir_gain(i)));
    end
    fvtool(htemp(:),'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); 
cfir_gain = cfir_gain(3)
if ShowPlots>=3 && use_cfir==1
    fvtool(cascade(hcfir,hcic,dfilt.scalar(1/(gain(hcic)*m_cic*cfir_gain))),...
           'Fs',[ fs_cic ]); axis([0 5 -200 +10]);
    title('CFIR-CIC Cascaded Magnitude Response (dB)');
    fvtool(cascade(hcic,dfilt.scalar(1/(gain(hcic)*m_cic))),...
           cascade(hcfir,dfilt.scalar(1/cfir_gain)),...
           cascade(hcfir,hcic,dfilt.scalar(1/(gain(hcic)*m_cic*cfir_gain))),...
           'Fs',[ fs_cic fs_cfir fs_cic ],...
           'Legend','off',...
           'ShowReference','off');
    axis([0 0.12 -0.1 +0.1]);   % Focus in on passband
    legend('CIC','CFIR','CIC-CFIR Cascade');
    title('Passband Zoom Overlay of CIC, CFIR and cascaded CFIR-CIC Magnitude Responses (dB)');
end

%% Create the PFIR
%  PFIR response should further attenuate the CIC lobe and sharpen
%  up the pass-band to stopband transition edge
pfir_use_firceqrip = 1;

% Set stop-band attenuation of Pulse-Shaping FIR; if using firceqrip with a 
% slope, start with a low basic stop-band attentuation, else go for higher
% stop-band
if cfir_use_firceqrip == 1
    ast_pfir = 60;
else
    ast_pfir = 85;   % Stopband attenuation of Compensation FIR
end    
for macs=1
    % Determine the available taps using the selected number of MAC units
    pfir_os = fclk/fs_pfir/n_ch;
    taps_pfir = (macs*pfir_os*4-1);
    n_pfir = taps_pfir-1;
    display(sprintf('PFIR tap count is %d, using %d MACs',taps_pfir,macs));
    if n_pfir < 30, error(sprintf('PFIR tap count of %d is too low, using %d MAC units!',taps_pfir,macs)); end

    for i=1:4
        if use_pfir==1

            if pfir_use_firceqrip==1
                ripple = 10^(apass/20);         % Maximum value of ripple
                err_pass = (ripple-1)/2;        % Ripple error
                ast    = 10^(-1*ast_pfir/20);   % Convert stop-band attenuation to weight
                slope  = 40;                    % Slope in stop-band, db/rad/sample
                wpass  = fpass/(fs_pfir/2);     % Normalized frequency pass-band edge

                pfir = firceqrip(...
                    n_pfir,wpass,[err_pass, ast],'passedge',...
                    'slope',slope);
                %pfir_gain(i) = m_pfir*scale_tweak(1);
                %pfir_scaled  = pfir*pfir_gain(i)
                [ pfir_scaled pfir_gain(i) ] = scale_coeffs(pfir,m_pfir);
                pfir_scaled = pfir_scaled*scale_tweak(1);
                pfir_gain(i) = pfir_gain(i)*scale_tweak(1);

                if m_pfir>1
                    hpfir(i) = mfilt.firinterp(m_pfir,pfir_scaled);
                else
                    hpfir(i) = dfilt.dffir(pfir_scaled);
                end
            else
                % Parks McLellan / Generalized Remez algorithm
                F = [0 fpass fstop 2*fstop 2*fstop fs_pfir/2]/(fs_pfir/2);
                A = [scale_tweak(1) scale_tweak(1) 0 0 0 0];
                W = [10 1 10];
                pfir= gremez(n_pfir,F,A,W);
                
                pfir_gain(i) = m_pfir*scale_tweak(1);
                pfir_scaled = pfir*pfir_gain(i);
                %[ pfir_scaled pfir_gain(i) ] = scale_coeffs(pfir,m_pfir);
                %pfir_scaled = pfir_scaled*scale_tweak(1);
                %pfir_gain(i) = pfir_gain(i)*scale_tweak(1);
                
                if m_pfir>1
                    hpfir(i) = mfilt.firinterp(m_pfir,pfir_scaled);
                else
                    hpfir(i) = dfilt.dffir(pfir_scaled);
                end
            end
            set(hpfir(i),...
                'Arithmetic','fixed',...
                'CoeffWordLength',18,...
                'FilterInternals','SpecifyPrecision','RoundMode','floor');
            if ShowPlots>=4
                fvtool(cascade(hpfir(i),dfilt.scalar(1/pfir_gain(i))),'Fs',[ fs_pfir ]);
                title(sprintf('PFIR Magnitude Response (dB) with N=%d, Ast=%d, firceqrip=%d',n_pfir,ast_pfir,pfir_use_firceqrip));
            end
        else
            hpfir(i) = dfilt.scalar(1);   % Bypass PFIR
            pfir_gain(i) = 1;
        end
        % Next loop adjustments
        ast_pfir=ast_pfir+10;
    end
end

% Display the loop results in an overlay
if ShowPlots>=4 && use_pfir==1
    % fvtool(pfir,'Fs',[ fs_pfir ]);
    for i=1:4
        htemp(i)=cascade(hpfir(i),dfilt.scalar(1/pfir_gain(i)));
    end
    fvtool(htemp(:),'Fs',[ fs_pfir ],'ShowReference','off');
    title('Overlay of PFIR Magnitude Responses (dB)');
end

% Choose an option from the loop and display selected response
hpfir = hpfir(3); pfir_gain = pfir_gain(3);
if ShowPlots>=3 && use_pfir==1
    fvtool(cascade(hpfir,dfilt.scalar(1/pfir_gain)),'Fs',[ fs_pfir ]);
    title('Selected PFIR Magnitude Response (dB)');
end

%% Filter cascade and overlay visualization
full_chain = cascade(hpfir,hcfir,hcic,dfilt.scalar(1/(gain(hcic)*m_cic*cfir_gain*pfir_gain)));
if ShowPlots>=1
    fvtool(full_chain,'Fs',[fs_cic]); axis([0 5 -200 10]);
    title('Final Cascaded Magnitude Response (dB)')
    fvtool(cascade(hcic,dfilt.scalar(1/(gain(hcic)*m_cic))),...
           cascade(hcfir,dfilt.scalar(1/cfir_gain)),...
           cascade(hpfir,dfilt.scalar(1/pfir_gain)),...
           full_chain,...
           'Fs',[fs_cic fs_cfir fs_pfir fs_cic],...
           'Legend','off',...
           'ShowReference','off');
    axis([0 10 -200 10]);
    legend('CIC','CFIR','PFIR','Full Cascade');
    title('Final Overlaid Magnitude Responses (dB)')
end