OPA376: Two OPA376 Distortion?

user6233088

Part Number: OPA376

Hi TI experts,

I met an issue when using OPA376, circuit is configured as below:

Supply voltage is 3V and GND, Vref is 400mV. signal source VG1 is a normal sine wave with hundreds of uV level.

when I connect voltage source J_P and J_N to J_PRE_P and J_PRE_N, the measured signal (VM) is like this: seems half of the sine wave is moved up and down.

while when I remove the first stage OPA376 (IOP1 and IOP2 in figure above), and only use the second stage OPA376 (IOP3 and IOP4 in figure above), with J_P and J_N connected to J_POST_P and J_POST_N,the signal becomes normal and no distortion:

This really confused me. What lead to the distortion when I add first stage? is it because

(1) offset? but OPA376 is also used in the second stage, why no distortion appeared?

(2) crossover? but why the second stage doesn't have crossover distortion?

any other possible reasons? how to explain this?

Thanks!

over 4 years ago

0 user6233088 over 4 years ago

Prodigy 40 points

please ignore some mistakes in the above circuit, it is only a diagrammatic sketch. the key issue is the distortion.

0 Thomas Kuehl over 4 years ago

TI__Guru* 93105 points

Hello user6233088,

It looks like your first amplifier stage may be going into slew rate limiting and as a result producing the observed distortion. The reason I think that may be the case is because of the triangulation of the sine wave.

We really need to see your exact OPA376 circuit with component values and have more information about the input signal characteristics; frequency, amplitude, etc. If we have that, we can likely figure out what is occurring in the circuit.

Regards, Thomas

Precision Amplifiers Applications Engineering

0 user6233088 over 4 years ago in reply to Thomas Kuehl

Prodigy 40 points

Hi Thomas,

The input signal frequency is quite low to 1Hz, hard to reach the SR limiting. Can you please give me your email address?

Thanks,

0 kai klaas69 over 4 years ago in reply to user6233088

Guru 140200 points

Hi Lz,

can you post your TSC file?

Kai

0 user6233088 over 4 years ago in reply to Thomas Kuehl

Prodigy 40 points

Hi Thomas,

Do you have the input voltage range data of OPA376 when MOSFET pairs swtching as the figure below shows (can be seen in your app note SBOA181A)?

Thanks

0 kai klaas69 over 4 years ago in reply to user6233088

Guru 140200 points

Hi Lz,

your distortion is way too big to be able to be explained by input offset voltage crossover.

The cause might be instability due to too high capacitive load or beginning short circuit protection or something else. But without schematic or any other further details is impossible to say something useful.

Kai

0 Thomas Kuehl over 4 years ago in reply to user6233088

TI__Guru* 93105 points

Hi LZ,

Is there a reason such as company proprietary information that you are unable to share your OPA376 circuit here on the e2e forum? We usually try to address inquires made to the e2e in the open so that all interested can learn from the inquiry. However, if you can't share your circuit due to proprietary reasons here we can take the matter private.

Regards, Thomas

Precision Amplifiers Applications Engineering

0 Thomas Kuehl over 4 years ago in reply to Thomas Kuehl

TI__Guru* 93105 points

Hi LZ,

Since this has been moved offline, please close this e2e thread.

Thanks, Thomas

Precision Amplifiers Applications Engineering

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OPA376: Two OPA376 Distortion?