DAC5672 Sine output

[Altera_Forum]

Hi All, 

 I am trying to generate a simple Sine wave from DAC5672 on my Hsmc daughter card from Terasic . The NCO i am using is from Open Cores , i works fine in simulation as shown in screen shot attached , But when i connect my scope probes i get distorted output screen shot attached . The DAC and NCO are provided with 100Mhz clock and the required output is 12Mhz , which is in my case is 12Mhz but distorted .  When is connect a simple upcounter , i get a Saw tooth wave output as expected .  Has anyone solved this problem ? is there something i am missing ?

[Altera_Forum]

Seems like you're providing wrong input to the DAC. Check if it expects you to give it complement 1s input?

[Altera_Forum]

I havent read anything about 14-bit inputs being 1's complement . 

The only mention about the inputs is given in the attached screen shot .

[Altera_Forum]

The 14-bit digital data input fallows the offset positive binary coding scheme. 

  Your turn to google now.

[Altera_Forum]

Really great idea.

[Altera_Forum]

Thanks for the guidance, now i need a VHDL function to convert 14-bit std_logic into off-set binary code, any ideas ?  

:)

[Altera_Forum]

Strange question from FPGA guru :) Seems like You only need to change MSB according to the value... Google for TI DAC interfaces pdf, there's a good explanation and examples.

[Altera_Forum]

Here's how i am changing values in VHDL 

 ADJUSTING_OFFSET: PROCESS(sys_clk, sin_out_reg) BEGIN  IF reset_n = '0' THEN  sin_out_adj <= (others=>'0');  ELSIF rising_edge(sys_clk) THEN   IF nco_sin_out(13) = '1' THEN   sin_out_adj <= NOT(nco_sin_out)+"00000000000001";  ELSE   sin_out_adj<= '1'& nco_sin_out(12 downto 0);  END IF;  END IF;  -- END IF;  END PROCESS;   But i am not getting a clean sine wave out ?? the frequency of generated signal is correct  see image attached

[Altera_Forum]

--- Quote Start ---  Here's how i am changing values in VHDL  ADJUSTING_OFFSET: PROCESS(sys_clk, sin_out_reg) BEGIN  IF reset_n = '0' THEN  sin_out_adj <= (others=>'0');  ELSIF rising_edge(sys_clk) THEN   IF nco_sin_out(13) = '1' THEN   sin_out_adj <= NOT(nco_sin_out)+"00000000000001";  ELSE   sin_out_adj<= '1'& nco_sin_out(12 downto 0);  END IF;  END IF;  -- END IF;  END PROCESS;   But i am not getting a clean sine wave out ?? the frequency of generated signal is correct  see image attached  --- Quote End ---    To change 2's complement to offset binary just invert the sign bit. sign_inv = not data(13); data <= sign_inv & data(12 downto 0);  keep this combinatorial to avoid latency problems

[Altera_Forum]

--- Quote Start ---  Hi All,  I am trying to generate a simple Sine wave from DAC5672 on my Hsmc daughter card from Terasic . The NCO i am using is from Open Cores , i works fine in simulation as shown in screen shot attached , But when i connect my scope probes i get distorted output screen shot attached . The DAC and NCO are provided with 100Mhz clock and the required output is 12Mhz , which is in my case is 12Mhz but distorted .  When is connect a simple upcounter , i get a Saw tooth wave output as expected .  Has anyone solved this problem ? is there something i am missing ?  --- Quote End ---   I can not send a private message to ask you a question. I'm in exactly the same situation how you have resolved the problem? my email yonatanhanann@gmail.com