Hello everybody!

I am currently working on making my own Multichannel AWG. Since the DAC I picked ( AD5547) outputs current, I am designing a simple current to voltage converter at the output. I want my voltage output swing to be +- 5 V . I have included a picture of my multisim simulation below. The output current of my DAC is 2mA and I know that with the feedback used in my design : Vout = 2mA * Rf so Rf = 2500 Ohms . Other than that I just have a couple of decoupling capacitors and a compensating capacitor in parallel with Rf. Also, for simplicity, I am just using one of my DAC's output. The output voltage that I get is not what I'm expecting. I have included my design below. Any help is appreciated.



Thanks.

 

A 50Ω load is low.
Can that op amp drive such a low resistance load?
A typical op amp load is no lower than 1k-2kΩ.

If you want a bipolar output, this is the circuit you should use:

 

Hello sir!
Thanks for the quick reply. I think you're right I will bump up my load resistance .
Also, I've looked at that schematic before but I don't quite understand the top portion of the design : why do they have -VREF going to the input of the DAC ?

 

why do they have -VREF going to the input of the DAC ?

To generate the negative output for a bipolar output.

Do you want a bipolar (AC centered around 0V) output?

 

Oh, I think I understand! I do want a bipolar output. I'll try to find a way to simulate that on multisim. I'll keep you updated.

Thanks again!

 

It is not -VREF. It is VREF inverted.

 

It is not -VREF. It is VREF inverted.

Yes, but that's how it's labeled on the schematic.

 

Alright, so I couldn't find a way to simulate the schematic from the AD5547 datasheet . However, I also realized that I had VDD and VSS switched on my design. Here's what I'm getting now with multisim :

 

The output is distorted
The load resistance is still likely too low.
Change RL to at least 500 ohms.

 

Yup! Changed it to a 1500 Ohms load and also increased the rail voltages :

 

Pardon my lack of familiarity with acronyms, but what sort of thing is an "AWG"?? I see one circuit with a D/A converter and an opamp, and other circuits with an opamp. so that leaves me a bit puzzled.

 

AWG = Arbitrary Waveform Generator ! The portion I'm working right now is the D/A converter . I'll link a good resource that helps me a ton in making mine here :
https://www.allaboutcircuits.com/pr...m-generator-analog-devices-ad9833-ATmega328p/

 

OK, that makes sense. Probably adding an adder arrangement could also produce a direct digital frequency Synthesizer . (DDS) The circuit does look reasonable, the challenge is always driving the low impedance load. Often that task is done with a pair of transistors in a complementary arrangement, which provides an additional benefit of being both easier and cheaper to replace in the event that the output stage is damaged by something that should not be connected.