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I designed a single-ended to differential signal amplifier using a tool provided by Texas Instruments:

calculation result

The source signal passes through a voltage follower (OPA810IDBVR), so the output resistance should basically be negligible. My problem is that there's an asymmetry, that is clearly visible in the oscillogram below (CH1 & CH2 = outputs, CH3 = input). The output signal is sent through the 1 meter long cable and is terminated with a LPF (\$33\Omega/22 pF\$ RC filter) before it's supplied to an ADC differential input. distorted waveform

Can you suggest me any possible cause of this problem? I also attach the application schematic (the voltage follower operational amplifier is outdated here): application schematic

Update 05/30/2024

I found the source of the problem - it was caused by exceeding voltage reference's max output current. After amplifying the current, this part of a problem was solved.

For anyone interested, there's the waveform of overloaded voltage reference's output in the photo (it should be stable \$1.50 V\$). : overloaded voltage reference's output

Unfortunately, my problem doesn't end here. Although the differential amplifier output is not distorted anymore, the gain factor of both channels is asymmetric. Each output channel \$V_{PP}\$ should be equal to \$1.00 V\$. asymmetric differential amplifier's gain I measured the equivalent resistances of both feedbacks and it's perfectly symmetric. However, I noticed that when I change the input signal from \$1.5 V_{PP} + 0.75 V_{DC}\$ to \$1 V_{PP} + 1 V_{DC}\$, it starts to look fine and the gain becomes exactly \$1.33 \dfrac{V}{V}\$ per channel. If anyone solved similar problem before, I'll be glad to read about your solutions, while I'm considering possible parameters' modification.

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1 Answer 1

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  1. Check your scope probes for correct compensation.
  2. Check that C4 and C9 are same capacitor values.

Update after OP edited question:
3. Check your supply rails are stable using the scope. Always. :-)

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  • \$\begingroup\$ The probes are fine - the signal doesn't change when I swap the probes. C4 and C9 values are the same, but I can test a couple of different values. \$\endgroup\$
    – drydre
    Commented May 28 at 20:25
  • \$\begingroup\$ What is output of IC1? \$\endgroup\$ Commented May 28 at 21:38
  • \$\begingroup\$ It's the exact same copy of its input - just like I meant it to run. \$\endgroup\$
    – drydre
    Commented May 28 at 21:44
  • \$\begingroup\$ Where were the scope probes placed? Were CH1 & CH2 right at the output pins of the U3? Where was CH3 placed? \$\endgroup\$ Commented May 28 at 21:55
  • \$\begingroup\$ Remove both C4 & C9 & repeat the waveforms of your post. Any difference? \$\endgroup\$ Commented May 28 at 22:01

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