DAC5674 EVM ???

EbuBad

Intellectual 290 points

Other Parts Discussed in Thread: DAC5674

Hey,

it is not clear that the pins of data should be 2C (compliment) or something else?

how can i generate a pure sine wave without negative value (2C values) from FPGA to DAC EVM?

should i use sinewave bits value without negative values?

Kind Rigards.

over 15 years ago

0 Hamza Fraz over 15 years ago

TI__Expert 5820 points

page 23 of datasheet:

The input data format is offset binary

Regards

0 EbuBad over 15 years ago in reply to Hamza Fraz

Intellectual 290 points

Thank you, i will try it for offset binary.

0 EbuBad over 15 years ago in reply to Hamza Fraz

Intellectual 290 points

Hey,

I just tried to see the spectrum of a two signal multiplication on spectrum analyzer via DAC5674

but as u know i multiplied the one msg signal and carrier signal => sin(wm)*sin(wc) and i must see the dirac(fc-fm) + dirac(fc+fm)

so i saw dirac(fc-fm)+dirac(fc)+dirac(fc+fm)

i dont wanna see dirac(fc).... so when trying the offset binary as it means (1+sin(wm))*(1+sin(wc)) so at the end

solution => 1 + sin(wm)+sin(wc)+sin(wm)*sin(wc)

and DAC dont understand the negative values... or maybe i dont know what i should to convert the decimal to binary....

Kind Regards.

0 Hamza Fraz over 15 years ago in reply to EbuBad

TI__Expert 5820 points

Ebubad

Did you multiply the signals digitally, before sending them into the DAC or are you using a modulator to upconvert DAC output to the carrier frequency?

If it is the latter case, you might be seeing 'LO feed through' in your output spectrum. Or their might be dc mismatch somewhere in the system that is being up converted to fc.

Regards

0 EbuBad over 15 years ago in reply to Hamza Fraz

Intellectual 290 points

I multiplied in digitally...

not use modulator.

Kind Regards.

0 Hamza Fraz over 15 years ago in reply to EbuBad

TI__Expert 5820 points

it sounds like something is not correct in your multiplication. Please refer to following MATLAB code

N = 32768
fs = 200e6
t = [0:N-1]/fs;
fin1 = 5e6
w1 = 2*pi*fin1
fin2 = 60e6
w2 = 2*pi*fin2
s = 0.975*sin(w1*t).*sin(w2*t);
s = round((1+s)/2 * 2^14);
S = (abs(fft(s)));
S = S(1:end/2);
f = [0:length(S)-1]/N*fs;
plot(f,20*log10(S))

0 EbuBad over 15 years ago in reply to Hamza Fraz

Intellectual 290 points

Hamza,

I converted the s by dec2bin(s) and sent the DAC

and i cant see the same plot in spectrum analyzer.

how should i convert that to offset binary?

Kind Regards.

0 Hamza Fraz over 15 years ago in reply to EbuBad

TI__Expert 5820 points

Ebubad

The code I provided you already generates offset binary data, no further conversion is necessary. You should feed the vector 's' to DAC

0 EbuBad over 15 years ago in reply to Hamza Fraz

Intellectual 290 points

Hamza,

Yeah i see that is for offset binary but it is decimal it must be convert to binary... so i used the dec2bin(s)

i should use binary data to send DAC by FPGA.

and spectrum is not the correct spectrum...

Kind Regards.

0 Hamza Fraz over 15 years ago in reply to EbuBad

TI__Expert 5820 points

Ebubad

How big is the magnitude of 'fc' signal? The operation of rounding (quantization) also creates an offset in the data which can be gotten rid of with dithering, if desired.

Regards

0 EbuBad over 15 years ago in reply to Hamza Fraz

Intellectual 290 points

Hamza,

if u ask magnitude of time-domain carier signal...

actually i dont multiple the signals in FPGA for ur matlab code. just use the s values binary data to see the same spectrum...

in ur matlab code i just use s with binary... and nothing the same

İf it is about frequency-domain carrier signal.

when i send the s to DAC i dont see the clear spectrum...i.e no fc or fm

Kind Regards.

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DAC5674 EVM ???