DSPRelated.com
Code
   Code Snippets    Submitted by tjc

Gray Code Generator - Matlab Script to Generate Verilog Header for Gray Coding

● November 2, 2010 ● Coded in Matlab 
%==============================================================================
%
%                   Gray Code Generator for Verilog
%
%   This script generates a Verilog header (.vh) file which contains a set of
%   of `define directives to establish Gray-coded states for a state machine.
%   The output of this script is intended to be used in conjunction with a
%   Verilog design which uses Gray coding in some application.  For more
%   information on Gray coding, please see 
%   http://mathworld.wolfram.com/GrayCode.html.
%
%   Usage: 
%
%       The bit width of the Gray coded states is set as a script variable.
%       2^bit_width states are generated.  The output filename is also 
%       set as a script variable.
%
%   Author: Tom Chatt
%
%------------------------------------------------------------------------------
% Revision History:
%
%   Original Version        Tom Chatt           11/2/2010
%
%==============================================================================

clear all; clc;

%------------------------------------------------------------------------------

bit_width = 8;  % Bit width of the generated code

% Print the generated code entries to a Verilog defines file?
print_to_v_def_file = true;

output_file = ['gray_code_',num2str(bit_width),'.vh']; % Output file name

% Gray code state name prefix.  State names will be of the form 
% GC<bit_width>B_<state number>.
prefix = ['GC',num2str(bit_width),'B_'];

%--------------Do not edit code below this point-------------------------------

% Generate the code, starting with 1 bit code and looping upward
code = [0; 1];
if bit_width ~= 1
    for i = 2 : bit_width
        code = [zeros(size(code,1), 1), code; ones(size(code,1), 1), flipud(code)]; %#ok<AGROW>
    end
end

% Print out the generated code
fid = fopen(output_file, 'w');

for i = 1 : size(code,1)
   
    macro_name = [prefix, num2str(i)];
    macro_val = [num2str(bit_width),'''', dec2bin(binvec2dec(code(i,:)),bit_width)];
    fprintf(fid, ['ifndef ',macro_name,'\n']);
    fprintf(fid, ['    ','`define ', macro_name, ' ', macro_val, '\n']);
    fprintf(fid, 'endif\n');
    
end

fclose('all');

CIC Filter Analysis script

● October 27, 2010●6 comments ● Coded in Matlab 
%==========================================================================
% CIC Filter Analysis Script
%
% Compute CIC filter frequency response, compensation filter coefficients,
% and compensated frequency response for a given set of design paramenters.
%
%
%   Author:  Tom Chatt
%
%   Revision History:
%==========================================================================
%   09/23/2010              Tom Chatt                   Initial Version
%==========================================================================

clear all; close all; clc;

%=============================
% CIC Filter Design Parameters
%=============================
N = 3;                     % Sinc/Comb-Filter order
M = 1;                     % Stage delay (should be 1 or 2).
D = 64;                    % Decimation factor
fs = 10e6;                 % Pre-decimation sampling Frequency
fs_lo = fs / D;            % Post-decimation sampling frequency

%==============================
% Compensator Design Parameters
%==============================

B = 12; % Compensator coefficient bit width

% fir2 parameters
fc = fs/D/2;      % Ideal cutoff frequency
L = 16;           % Filter order - 1. Must be even. Final filter length is L + 1.
Fo = D*fc/fs;     % Normalized cutoff frequency

%=====================================================
% Generate and plot filters
%
% Floating point compensator filter coef. stored in h
% Fixed point compensator filter coef. stored in hz
%
%======================================================

% CIC Compensator using fir2
p = 2e3;                    % Granularity
s = 0.25 / p;               % Step size
fpass = 0:s:Fo;             % Pass band frequency samples
fstop = (Fo + s) : s : 0.5; % Stop band frequency samples
ff = [fpass fstop] * 2;     % Normalized frequency samples, 0 <= f <= 1

Mp = ones(1,length(fpass)); %% Pass band response; Mp(1)=1
Mp(2:end) = abs( M*D*sin(pi*fpass(2:end)/D)./sin(pi*M*fpass(2:end))).^N;
Mf = [Mp zeros(1,length(fstop))];
ff(end) = 1;
h = fir2(L,ff,Mf); %% Filter length L+1
h = h/max(h); %% Floating point coefficients
hz = round(h*power(2,B-1)-1)/(2^(B-1)); %% Fixed point coefficients

f = linspace(0,1,4*length(ff));
f_lo = [ff ff+1 ff+2 ff+3];
H = (D^-N*abs(D*M*sin(pi*M*D*f) ./ (pi*M*D*f)).^N);
HH = (D^-N*abs(D*M*sin(pi*M*ff) ./ (pi*M*ff)).^N);
HHH = (D^-N*abs(D*M*sin(pi*M*f_lo) ./ (pi*M*f_lo)).^N);

H_comp = abs(fft(hz,length(ff)));

%=========
% Plotting
%=========

figure('name','CIC Frequency Response','Numbertitle','off');
subplot(211);
plot(f*fs, db(H), 'b');
grid on;
title([{'Wideband frequency response of CIC filter'};{sprintf('D = %i, N = %i',D,N)}]);
xlabel('Frequency (Hz)');
ylabel('|H(e^{j\omega})| (dB)');
axis([0,fs,-1250,0]);

subplot(212);
plot(f_lo*fs_lo, db(HHH));
grid on;
title('Narrowband frequency response of CIC filter');
xlabel('Frequency (Hz)');
ylabel('|H(e^{j\omega})| (dB)');
axis([0,4*fs_lo,-200,5]);

figure('name','CIC with Compensator Filter','Numbertitle','off');
subplot(211);
hold on;
grid on;
plot(f_lo*fs_lo, db(HHH), 'b');
plot(f_lo*fs_lo, db([H_comp H_comp H_comp H_comp]), 'g');
plot(f_lo*fs_lo, db(HHH .* [H_comp H_comp H_comp H_comp]), 'r');
axis([0,4*fs_lo,-200,25])
title([{'CIC with Compensator FIR'};{sprintf('Compensator length = %i, Coefficient precision = %i',L,B)}]);
xlabel('Frequency (Hz)');
ylabel('|H(e^{j\omega})| (dB)');

subplot(212);
hold on;
grid on;
plot(ff*fs_lo, HH, 'b');
plot(ff*fs_lo, H_comp, 'g');
plot(ff*fs_lo, HH .* H_comp, 'r');
axis([0,1*fs_lo,0,1.1]);
title('Closeup of CIC + compensator passband');
xlabel('Frequency (Hz)');
ylabel('|H(e^{j\omega})|');
legend('CIC','Compensator Filter','Net Response','location','northeast');