Thanks for involvement. I will make a list of suggestions and comments from my side what is the effect, whether it improved operation or not.
The trouble is likely to be in your breadboard wiring.
OPA548 is a fairly high powered opamp, with upto 60 between it's power pins and it can deliver upto 3A dc.
https://www.ti.com/lit/ds/symlink/opa548.pdf
How is the GND current routed after it goes through the 30 Ohm resistor back to the power supply circuit?
To answer this question I am adding the view of the breadboard and my connections:
Figure 1: breadboard from the top
Figure 2: breadboard connections to the signal gen and oscilloscope
It's not clipping, the +/-5V supplies will deliver 6Vpp just fine, twice what is shown.
But do show layout, just in case.
Here above is the breadboard view as asked.
Try ramping the supply up to, say, ±10V and see what you get. I know it's not obviously clipping, but I've known op amps exhibit 'odd' behaviour when pushed into the corners of their performance envelopes before.
Tried this, changing voltage to +-12V does not solve the problem. All the other uploaded pictures are at the operation with +-12V supply.
You'll get a much better feel for the stability of the amp if you feed it some square waves and see what they look like.
You are very right here. When I switched to a square wave gen, the problem became more than obvious. Let's have a look at the figure 3.
Figure 3: square wave at 10kHz frequency with 30 ohm load.
But the kind of instability you have found in the literature isnt whats going on with your setup / amplifier. What you have isnt oscillating, it has a non symmetrical distortion.
Does this distortion become less as you make the 30 ohm load higher - try 300, but keep same frequency and amplitude. Is it improved? Whats the supply rails? (Edit Cerebus has it, min supply issue)
You are right, now I see it can be distortion problem.
I have made a typo on my first post saying load of 10 kOhm (not 10 kHz). So, yeah, when the load increases, the distortion effect significantly reduces (but don't completely vanish with 10 kOhm). If you go to open output, then there is not distortion. The problem is that in my application small loads need to be driven (15 Ohm to 1 kOhm).
Yes, looks a bit like crossover distortion.
As I found out it very much is a crossover distortion. Check the video attached below.
Suspect UHF oscillation that is on the distorted part of wave and invisible as above max freq capability the scope and probe. The oscillation changes the bias conditions.
Check power bypass caps at pins of opamp, perhaps add a damping RC at output.
Jon
Scope is capable of 200MHz and it is nowhere near the limits. Tried RC snubber, does not help.
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It's not clipping, the +/-5V supplies will deliver 6Vpp just fine, twice what is shown.
No reason to believe it's oscillation, the scope doesn't show anything obvious (but, it's in averaging mode, how many averages? and why?), and there aren't other errors like DC shift or distortion.
But do show layout, just in case.
If a bias resistor, say 220 ohms from +5V, or -5V, to output, changes the position of the hiccup, it's definitely crossover distortion.
Hey Tim, your answer helped to diagnose the problem. Check the attached video for the crossover effect.
Averaging on the scope is turned on for 2 cycles. it helps to reduce white noise.
There is no DC shift and I have enough supply for the opamp to not start clipping the waveform (+-12V supply voltage).
When I add a resistor as you say between the output and -5V or +5V supply rail, the hiccup position moves and it once again proves the
crossover distortion problem.
The link to the video:
https://photos.app.goo.gl/zQ89u8tnV5SJdncV9. In the attached video I change the input signal offset. The input peak to peak is 1V. Th offset move between -0.6 to +0.6 and it shows that the hiccup disappears when the waveform leaves the negative voltage area or goes below the hiccup level.
Now we identified the issue - it is
CROSSOVER DISTORTION. What are the ways to solve it? I assume it some sort of biasing problem inside the opamp. Is the only way to change the opamp to a better one? I am powering a reference resistor and electrodes, so I have mainly resistive loading. A simple example schematic of the load is below.
Figure 4: the load.
Any help and suggestions would be appreciated! and thank you guys who already helped me a lot!