How do I control ZMOD DAC 1411 (AWG) output voltage levels? (High/Low gain setting? CA? CG?)

[B. Nasir Ashfaq]

Hello, I am using ZMOD DAC with Eclypse Z-7 board, and I have two questions regarding controlling ZMOD DAC 1411 output voltage:

1) How do I switch between the low gain and high gain setting in ZMOD AWG (ZMOD DAC 1411) to shift between +/-1.25V and +/- 5V setting using the ZMOD DAC LLC IP in Vivado?

2) I want to control the output voltage levels of the DAC. How do I change the signed 14-bit values in my Verilog module to achieve the desired output voltage? The reference manual shows the following equation for controlling the 14 bit value:

So for example, if I want to have voltages between 0 and 3 V, how do I set CA, CG and Range (which is again related to High/Low gain value from Q1 above) values using LLC IP in Vivado? How do I interpret Vout in this case? The LLC IP shows as follows:

 

Please provide me with some help in this regard. Currently, I am giving between 14'd0 and 14'b01111111111111 and I am only seeing between 0-670 mV on oscilloscope with trigger setting of 50 ohm DC (and ~0-1.3 V with trigger setting of 1 M ohm DC).

Please let me know if you need more information from me.

Thank you,

Nasir

 

[zygot]

The AD9717 is a DAC designed for communications and waveform generation. It's not clear from you post if you want to create a static output or just limit the swing of a waveform.

You've started off with the correct documentation, which is the ZMOD1411 Reference Manual, so read and understand that document as well as the AD9717 datasheet.

To constrain the analog buffer output swing you have a few general options:

1. You can limit the DAC input word to the desired low and high values that correspond to your output requirements. This approach basically uses only part of the DACs dynamic range, and therefore limits the number of values that the output can be set to. There are a few ways to accomplish this. Your software application can handle this or you could use a multiplier in your low lever design to scale the output. It's not too hard to
2. You can use the ZMOD1411 output to drive another amplifier that converts the signal to the desired output span. This approach requires some analog design skills but preserves the entire DAC dynamic range.

There's a relay on the ZMOD1411 pod to switch between high and low output scales using the SET_FS inputs. Refer to the low level controller documentation.

The ZMOD1411 is designed to put out a signal centered around 0V. This signal could drive a separate amplifier that adds an offset using option 2 from above.

If you want a static digitally controlled output voltage there might be better options.

ADC and DAC devices have different architectures and general approaches that are optimal for particular applications. Trying to shoehorn a particular device into an application for which is isn't designed is problematic.