TL974-Q1: Output idle noise check

Alpha Han

Expert 3750 points

Part Number: TL974-Q1
Other Parts Discussed in Thread: OPA1612-Q1

Hi, Team:

My customer use TL974-Q1 and find some part output noise is about 3uV but some part output noise is about 9.1uV.

Can you help to check and advise if any parameters can show this performance? and if you can help to verify this?

Test Condition:

AP525, A-weighting, 20-20KHz filter, no audio input.

Some part test result 3uV

NG part test result 9.1uV.

over 1 year ago

0 Jerry Madalvanos over 1 year ago

TI__Mastermind 24851 points

Hey Alpha,

The TL974-Q1 has typical noise specified at 4nv/rtHz for typical specifications you can expect to see variations higher and lower than the typical spec. There is not a max noise specification for noise.

See section 7.3.9 in the below datasheet for estimation from typical spec.

https://www.ti.com/lit/ds/symlink/opa2990.pdf

How many devices are you seeing this noise result at?

Additionally, if you require a device with a noise spec that is below a certain value, ensure that the noise specification in the datasheet has a maximum value, as these will be a tested limit to ensure the part is below that limit.

Best,
Jerry

0 Alpha Han over 1 year ago in reply to Jerry Madalvanos

TI__Expert 3750 points

Hi, Jerry:

Thanks for your feedback. Then for TL974-Q1, looks like we have only mean value µ as it's mean is not 0. What's the σ value?

Besides, can you help to recommend a AEC-Q100 amps with maximum noise parameters in datasheet and can achieve 3uV idea noise in above test condition?

0 Jerry Madalvanos over 1 year ago in reply to Alpha Han

TI__Mastermind 24851 points

Alpha,

I will look into what the σ value is. I also have a couple questions.

How many devices are you seeing higher noise on?
Could you share the schematic of the filter?

Best,
Jerry

0 Alpha Han over 1 year ago in reply to Jerry Madalvanos

TI__Expert 3750 points

Hi, Jerry:

Please find below feedback;

How many devices are you seeing higher noise on?
1. We found 21 pcs in total of 900 pcs
Could you share the schematic of the filter?
1. Please refer attached file.

0 Jerry Madalvanos over 1 year ago in reply to Alpha Han

TI__Mastermind 24851 points

Hey Alpha,

TL974Q is our lowest noise quad op amp in automotive . If you want a lower noise option you will need to use a dual op amp. OPA1612-Q1 is a 1.1nV/rtHz op amp.

Best,
Jerry

+1 Jerry Madalvanos over 1 year ago in reply to Jerry Madalvanos

TI__Mastermind 24851 points

Additionally, your passives can contribute a significant amount of noise. Doing a quick root sum square, your passives can contribute an additional ~1uVrms if your amplifier is 3uVrms, and the specification is 4nV/rtHz at 100kHz, which is your broadband noise. Your bandwidth includes flicker noise which can contribute a significant amount to your total noise.

Best,
Jerry

0 Alpha Han over 1 year ago in reply to Jerry Madalvanos

TI__Expert 3750 points

Hi，Jerry:

Are you able to find what the σ value is?

0 Jerry Madalvanos over 1 year ago in reply to Alpha Han

TI__Mastermind 24851 points

Hey Alpha,

The sigma values vary from device to device, and I was unable to track down this exact device sigma value. Our general rule of thumb for some design guidelines is about +/-30% to give ample overhead.

Best,
Jerry

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TL974-Q1: Output idle noise check