I am trying to create a sawtooth waveform using microcontroller/counter and DAC. Instead of getting a nice smooth ramp, I am getting a ramp but with impulses and other noise. I am using AD7533 DAC and AD8055 Op Amp. The 10 bit input comes from a microcontroller. I am interfacing the DAC using figure11 from dac's datasheet:
Considering the note under the drawing, I decided to omit R1 and R2 from the circuit and made it the following way:
When I measure the signal at the negative terminal of the OpAmp, I get this reading:
which is not that attractive. Changing Vref does not make much difference. At Vref=5V the signal on the negative OpAmp input looks like this:
When I measure the signal on the OpAmp output pin, it looks like saturated:
So, two questions:
Am I missing some trivial components? Why the signal looks so bad?
Why OpAmp gets saturated if I do not do any gain? Moreover, the signal is withing 0-3V range and the power on the OpAmp is 5V.
EDIT: So, I considered suggestions from the comments (shorted R2 and added negative rail to OpAmp power) and there I am getting this waveform:
It still looks very noisy and when I zoomed it in, the ramp also looks to float up and down:
Theoretically, since my range is about 3.3V peak to peak, and given 10 bit resolution, the output signal should have resolution of 3.3mV. Whereas, the noise is as bad as 100mV. Any practical approaches on how to fight this noise?
Also, my next stage is going to be AD8531. I will use it as a high current G=1 buffer - the output from the AD8055 will be connected to +in of the AD8531. Do I need to place the load resistor to ground between the two amps, or connect the output to the input directly?