OPA2187: Offset voltage varies non-linearly with input common mode voltage (within the specification)

Shinichi Inoue

Guru 22446 points

Part Number: OPA2187

Dear Specialists,

My customer is evaluating OPA2187 and has a question regarding offset voltage vs Vcm.

The offset voltage varies non-linealy with input common mode voltage.(within the spec <15uV)

I would be grateful if you could advise.

I would like to share the information, but it is a confidential.

Could you please send a friendship request?

I appreciate your great help in advance.

Best regards,

Shinichi

1 month ago

0 Chris Featherstone 1 month ago

TI__Mastermind 30835 points

Hello,

Our support engineer for this product will be returning on Monday. Have you compared the measured data to the plot in the product datasheet? How does it compare?

Best Regards,
Chris Featherstone

0 Shinichi Inoue 29 days ago in reply to Chris Featherstone

Guru 22446 points

Hi Chris,

Thank you for your reply.

The customer measured the output voltage and divided the gain.

The offset voltage is within the spec, but there are non-linearity.

I sent a schematic and waveform to the your private message.

Could you please see and advise what is the cause of non-linearity?

If the file is not delivered, could you please let me know.

I appreciate your great help and cooperation.

Best regards,

Shinichi

0 Chris Featherstone 28 days ago in reply to Shinichi Inoue

TI__Mastermind 30835 points

Hello,

The OPA2187 is a chopper amplifier that has very low offset voltage. This low offset voltage is achieved through the use of internal calibration MOSFET switches to alternately switch the inputs. However, this calibration technique generates current transients within the amplifiers input bias current. These transients flow through the amplifiers feedback network and source impedance generating additional offset voltage, offset drift, and transient noise tones. The magnitude of this error increases when large feedback resistances or source impedances are used. Furthermore, this error is dependent on the details of the chopper amplifier design, so that some products are more susceptible to Vos shift than others.

I would recommend looking over this detailed application note below on Optimizing Chopper Amplifier Accuracy. The OPAx187 is covered in the paper below and I believe you are experiencing the Vos behavior due to component values surrounding the amplifier.

https://www.ti.com/lit/wp/sboa586a/sboa586a.pdf?ts=1781549965358&ref_url=https%253A%252F%252Fwww.google.com%252F

Let us know if you have any further questions.

Best Regards,
Chris Featherstone

0 Shinichi Inoue 28 days ago in reply to Chris Featherstone

Guru 22446 points

Hi Chris,

Thank you for your reply.

I sent additional questions to private message.

Could you please see and advise?

I appreciate your great help and cooperation.

Best regards,

Shinichi

0 Chris Featherstone 27 days ago in reply to Shinichi Inoue

TI__Mastermind 30835 points

Hi Shinici,

I have seen your additional comments in the private chat. I will look them over.

Best Regards,
Chris Featherstone

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OPA2187: Offset voltage varies non-linearly with input common mode voltage (within the specification)