Issues generating 4 DDS sine waves with independently variable amplitude, phase, and frequency

Hi Vishwanath ,

Thank you for your interest in AD9106. Each DAC channel can independently control gain and phase based on the on-chip DDS. However, the 4 DACs cannot have different frequencies if the on-chip DDS is used because, as you mentioned, the DDS is a global shared resource. To generate different frequencies for each channel, you must generate a sinewave using the on-chip SRAM, and each channel will have an allocated start/stop address. Related query here: (+) Output different frequencise on AD9106 - Q&A - High-Speed DACs - EngineerZone (analog.com). More details on Page 27 of the datasheet. 

Also, the DDS tuning word only affects frequency, not the amplitude of the waveform. It's likely that there is a component in your output datapath that has a certain bandwidth so increasing the frequency attenuates your waveform. Can you share your schematic? If all the 4 DAC datapaths are identical, the outputs in the 4 channels should be the same.

Also, if a register will not be used in your application, please set it to its default value as it will likely have an effect on your waveform. For instance, Register 0x0E is set to 0 when is should be set to 0x0E. 

Best regards,
Marco

Hello, 

Thanks for your response. We are using the EVAL-AD9106 board as a shield for an Arduino UNO R3. It is mounted directly onto the Arduino which is powered by USB. We will look into using the SRAM to modulate the sine wave frequencies individually.

We also uploaded example 3 from the AD9106 data sheet using the register values from this example code and observed that DAC2 still outputs around 10x less voltage than the 3 other DACs. We are concerned that the output may be broken somehow, but aren't sure how to check. 

Thanks

Hello, 

Thanks for your response. We are using the EVAL-AD9106 board as a shield for an Arduino UNO R3. It is mounted directly onto the Arduino which is powered by USB. We will look into using the SRAM to modulate the sine wave frequencies individually.

We also uploaded example 3 from the AD9106 data sheet using the register values from this example code and observed that DAC2 still outputs around 10x less voltage than the 3 other DACs. We are concerned that the output may be broken somehow, but aren't sure how to check. 

Thanks

Hi Vishwanath ,

For creating the sine wave vector to be written onto the SRAM, you may use any pattern generator softwares. For ADI, we have the ACE Vector Generator Tool (found thru this link: ACE Software). This can generate the vector to be stored in SRAM so that you could configure the waveform to your liking (amplitude, frequency, type of waveform, data format, etc.). See FAQ#10 in this link for more details. 

In the AD9106 evaluation board, are you using the Balun output or the Amplifier output? Can you try testing the output in both cases (refer to AD9106 & AD9102 Evaluation Boards [Analog Devices Wiki] for the board connections) and see if the that fixes your issue? The AD9106 datapaths are all the same in the evaluation board so there should be no issue there. It's likely there is a problem with your system (e.g. connections to the Arduino Uno, code, etc.). The MBED example code provided is not tested using an Arduino Uno, rather we used the SDP-K1 Evaluation Board | Analog Devices which is used as a pair with AD9106. Unfortunately, I can't test this case on my side because I don't have an Arduino Uno. 

If the voltage is still less for DAC2 on both cases stated (Balun/Amplifier outputs), please try generating the sinusoid using the SRAM then see if the issue still persists. 

Best regards~

Hello, we reconfigured the board to output through the on-board amplifiers. The DAC2 issue still persists, it outputs much less voltage than the other DACs and is noticeably less stable than the other DACs when observed on an oscilloscope. However, the previous amplitude issues have been somewhat mitigated, although we still see slight changes in amplitude when we go from the kHz to Hz range. We also noticed that phase changes with frequency, which is unideal. Ultimately, we want to be able to control the amplitude, phase and global frequency of the 4 waves all independently of each other.

Our use-case involves producing waves with frequencies ranging from 2Hz-2kHz. Is there a way we can obtain better low-frequency performance with this board?

Beyond that, we noticed that the waves start clipping when the DGAIN register is set past 0x4000. According to Q14 from this forum , it seems that clipping will occur if the (digital data x digital gain) + digital offset > full scale current. We are wondering if in our setup, clipping is expected to occur after 0x4000. Our digital offset is 0 and our digital data is the DDS output, but we are unsure how to get an exact value on that. Moreover, we had trouble determining Ioutfsx = Vrefio/Rsetx. The register values we are using set the REFADJ register (0x03) to 0x0, which we believe corresponds to Vrefio = 1.04V according to Figure 37 in the AD9106 datasheet. However, the Rsetx values controlled by the FSADJ registers are set to 0x1f000 which differs from the reset value.