How do I Set Up DAC 5687 EVM Board?

1. I have verified the data that I wrote to the EVM board correctly at RP5, 6, 9 and 10.  I am writing at the data rate of 16 Mhz.  When I write 0x0 to the DAC and both of the analog output of Channels A and B show 0.  However, I cannot tell the difference of the analog output when writing 0x7FFF7FFF to the DAC.  I write other non-zero values.  Also show the same thing.  (I cannot tell the difference.)  I am hooking up the clock with my source clock, which runs at 84 Mhz.  What could be wrong?  Do I need a faster input clock?  How fast?  I have verified the 1.8 V and 3.3 V power supply to the board correctly.  I used SPI control software from TI to turn on FULL/FIR/FIFO Bypass only.

Reply>> if you input is static, i.e. the data is not changing clock cycle to clock cycle, then the output will be static. The DAC5687EVM is configured in its default configuration for an AC coupled output through a transformer, which acts as a high pass filter with a couple 100 kHz bandwidth. The static or DC signal will not pass through the transformer, and the transformer center tap will remove the DC signal at the DAC output pins.

Please refer to section 2.2 of the User's guide for a setup procedure for testing the EVM with only a clock signal (no data connection). You should be able to see the same result as shown in the user's guide.

Once you verify that, then we can work on how to continue.

Robert

And when you are ready to input a CW signal, you can use the attached image to load DAC register accordingly (as an example).

Hi Robert and Hamza,

I have followed 2.2 setup.  I can see clock wave with NCO turned on.  Thanks for pointing out the EVM acts as a high pass filter with a couple 100 kHz bandwidth.  Now I was able to generate some analog signals on the output end.  The thing is I was not able to generate saw  tooth or sine wave forms.   There might be some formula that I have to follow instead of keeping incrementing the variable and writing to the DAC input port to generate saw tooth.  Sine wave generation might be more involved.  I confirmed that my writing frequency is consistent with the analog output by changing the A channel DAC input data twice faster than data feeding into the B channel.  I will very appreciate if you can show me how to generate the sawtooth and sine wave forms.  Thanks!

Jew-Dong

You can use the following MATLAB code for generating CW signal. You also might want to take a look at our pattern generator card that can drive all TI DACs with a CW/modulated signal. (http://focus.ti.com/docs/toolsw/folders/print/tsw3100evm.html)

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clear, clc, close all;

Fupdate = 200e6;     % Sample rate
samples = 2^16;      % Number of samples 

resolution = 16;    % Resolution

tones = [20.1e6];   % Array with the frequency of the tones to be generated

% Quantize frequencies
num_tones = length(tones);
for i = 1:num_tones
    if tones(i) > 0
        %freq(i) = tones(i);
        freq(i) = max(primes(round(tones(i)/Fupdate*samples)))/samples*Fupdate;
        F(i) = cellstr(strcat(num2str(freq(i)/1e6),'MHz_'));
    else
        freq(i) = -max(primes(round(abs(tones(i))/Fupdate*samples)))/samples*Fupdate;
        F(i) = cellstr(strcat('m',num2str(-freq(i)/1e6),'MHz_'));
    end
end

freq        % Display exact frequencies being generated

% Generate complex exponential
n = 1:samples;
exp_arg = (j*2*pi/Fupdate)*(freq'*n);

if num_tones == 1
    complex_exp = exp(exp_arg);
else
    complex_exp = sum(exp(exp_arg));
end

IFout_i = real(complex_exp);
IFout_q = imag(complex_exp);

% Quantize the complex exponential to the bit resolution specified
maxAbs  = max(max(abs(IFout_i)),max(abs(IFout_q)));

scale = 0.99;
% scale = 10^(-0.1/20);
scale = scale*(2^(resolution-1))/maxAbs;

DACout_i = round(scale*IFout_i) + 2^(resolution-1) - 32768;
DACout_q = round(scale*IFout_q) + 2^(resolution-1) - 32768;

data = complex(DACout_i, DACout_q);

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