altera_cic_compensate_ip.m

级联积分梳妆滤波器的补偿滤波器

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%%
%% Generated by: CIC 7.2 Build 151 October, 2007
%% Generated on: 2008-4-15 17:59:26
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
% ratechangecic_core_fir_comp_coeff genearats CIC compensation filter coefficients
% using frequency sampling method.
%
%    ratechangecic_core_fir_comp_coeff(L, Fs, Fc, plot, is_fxp, B) calculates compensation
%    filter coefficients and saves the coefficients to a file.
%
%    L      - FIR filter length (= number of taps = number of coefficients)
%    Fs     - FIR filter sample rate in Hz before decimation
%    Fc     - FIR filter cutoff frequency in Hz
%    plot   - True or false to draw filter responses graphically
%    is_fxp - Indicating if the coefficients should be saved as fixed point or floating point numbers
%    B      - Number of bits to represent the coefficients if is_fxp is true
%
%    Examples:
%    ratechangecic_core_fir_comp_coeff(31,80e6,4e6,true,true,16);
%    ratechangecic_core_fir_comp_coeff(31,80e6,4e6,true,false)

function ratechangecic_core_fir_comp_coeff(L, Fs, Fc, plot, is_fxp, B)
try
% Validate number of input arguments
error(nargchk(0, 6, nargin));
%%%%%% CIC filter parameters %%%%%%
R = 2;     %% Decimation factor
M = 1;     %% Differential Delay
N = 5;     %% Number of Stages

%%%%%% User Parameters %%%%%%
% Check if Signal Processing Toolbox is in the Matlab installation
if (isempty(which('fir2')))
  error('Matlab Signal Processing Toolbox isn''t installed on your machine. Please contact Altera for help.');
end

%% Get user parameters: B, L, Fs, Fc if they aren't passed as arguments.
if(nargin < 1)
     %% Filter length: it must be an odd number, otherwise it'll be increased by 1.
  L = input('Number of filter coefficients (31 as default): ');
  if isempty(L)
   L = 12;                             
  end
    end
if mod(L,2) == 0
  fprintf('FIR filter length must be an odd number. %d is used instead.\n',L+1);
  L = L+1;
end
    
    
if(nargin < 2)
     %% FIR filter sample rate in Hz before decimation
  Fs = input('FIR filter sample rate in Hz before decimation (80e6 as default): ');
  if isempty(Fs)
      Fs = 80000;
     end
end
  
if(nargin < 3)
     %% FIR filter cutoff frequency in Hz
  Fc = input('FIR filter cutoff frequency in Hz (4e6 as default): ');
  if isempty(Fc)
   Fc = 4000;
     end
    end
    
    if (nargin < 4)
     plot_res = input('Do you want to plot filter responses? Y/N [N]:','s');
  if isempty(plot_res)
   plot_res = 'N';
  end
  if upper(plot_res) == 'Y'
   plot = true;
  else
   plot = false;
  end
    end
    
if(nargin < 5)
  fxp_coeff = input('Do you want to write out coefficients as fixed point numbers? Y/N [Y]:','s');
  if isempty(fxp_coeff)
   fxp_coeff = 'Y';
  end
  if upper(fxp_coeff) == 'Y'
   is_fxp = true;
  else
   is_fxp = false;
  end
    end

if(is_fxp && nargin < 6)
  %% Number of bits to represent fixed point filter coefficients
  B = input('Number of bits to represent the filter coefficients (16 as default): ');
  if isempty(B)
      B = 8;
     end
end
  
Fo = R*Fc/Fs;                            %% Normalized Cutoff freq; 0<Fo<=0.5/M; 
                                          %% Fo should be less than 1/(4M) for good performance                              
% Fo = 0.5/M;                            %% use Fo=0.5 if we don't care responses outside passband

%%%%%%% CIC Compensator Design using fir2.m %%%%%%
p = 2e3;                                 %% Granulatiry
s = 0.25/p;                              %% Stepsize
fp = [0:s:Fo];                           %% Passband frequency samples                                        
fs = (Fo+s):s:0.5;                       %% Stopband frequency samples
f = [fp fs]*2;                           %% Noramlized frequency samples; 0<=f<=1; 
Mp = ones(1,length(fp));                 %% Passband response; Mp(1)=1
Mp(2:end) = abs( M*R*sin(pi*fp(2:end)/R)./sin(pi*M*fp(2:end))).^N; %% Inverse sinc
Mf = [Mp zeros(1,length(fs))];
f(end) = 1;
h = fir2(L-1,f,Mf);                      %% Filter order = filter length (L) - 1
h = h/max(h);                            %% Floating point coefficients, scaled it to 1

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Output filter coefficients to a file for Altera FIR Compiler           %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

filename = 'ratechangecic_core_fir_comp_coeff.txt';
fid = fopen(filename, 'wt');
if (fid == -1)
  errMsg = sprintf('Can''t Open file %s for writing.\n', FileName);
  error(errMsg);
end;

if (is_fxp) % coefficients are fixed point
  hz = fix(h*(2^(B-1)-1));               %% Quantization of filter coefficients
  fprintf(fid, '%d\n', hz); %% fixed point coeff
else
  fprintf(fid, '%.6f\n',h); %% floating point
end
fclose(fid);

fprintf('The compensation filter coefficients have been saved to file ''%s''.\n',filename);

% Change the following variable to 1 if you would like to plot the filter responses

if (plot)
  if (is_fxp)
   plot_responses(R,M,N,hz,Fs,is_fxp);
  else
   plot_responses(R,M,N,h,Fs,is_fxp);
  end
end;
catch
rethrow(lasterror);
end;
%% Function for ploting filter responses
function plot_responses(R,M,N,res,Fs,is_fxp)
try
%%%%%%% Full resolution CIC filter response %%%%%%%%
hrec = ones(1,R*M);
tmph = hrec;

for k=1:N-1
     tmph = conv(hrec, tmph);
end;
hcic = tmph;
hcic = hcic/max(hcic);

%%%%%%% Total Response %%%%%%%%%%%%%%%
resp = upsample(res, R);
ht = conv(hcic, resp);              %% Concatenation of CIC and fir2 FIR at high freqency

no_data_points = 4096;              %% Number of data points to plot in the figure

[Hcic, wt] = freqz(hcic, 1, no_data_points, Fs);      %% CIC Freq. Response
[Hciccomp, wt] = freqz(resp, 1, no_data_points, Fs);  %% CIC Comp. response using fir2
[Ht, wt] = freqz(ht, 1, no_data_points, Fs);          %% Total response for CIC + Compensation fir2

warning off all;                                      %% Turn the 'Log by zero' warning off
Mcic = 20*log10(abs(Hcic)/(abs(Hcic(1))));            %% CIC Freq. Response
Mciccomp = 20*log10(abs(Hciccomp)/(abs(Hciccomp(1))));%% CIC Comp. response using fir2
Mt = 20*log10(abs(Ht)/(abs(Ht(1))));                  %% Total response for CIC + Compensation fir2
warning on;                                           %% Turn warnings on

figure;
plot(wt, Mcic, wt, Mciccomp, wt, Mt);
if (is_fxp) % coefficients are fixed point
  legend('CIC','CIC Comp','Total Response (Fixed Point)');
else % floating point
  legend('CIC','CIC Comp','Total Response (Floating Point)');
end
ymax = max(Mciccomp)+1;
ylim([-100 ymax]);
title('CIC and its Compensation Filter Responses');
grid;
xlabel('Frequency Hz');
ylabel('Filter Magnitude Response dB');
catch
rethrow(lasterror);
end;