LMH6703: Bypass capacitor between ±Vs supplies

Narek

Part Number: LMH6703

Hello. I would like to know whether or not a bypass capacitor is required to be connected across the V+ and V- supplies in a dual-supply application. I've read that this helps with 2nd harmonic distortion generally for dual-supply opamps. Any literature recommendation that dives into this in more detail would be most appreciated.

Thanks.

over 1 year ago

0 Alec Saebeler over 1 year ago

TI__Mastermind 24529 points

Hello Narek,

I found a few resources for you:

https://www.eetimes.com/bypass-or-decouple-your-way-to-power-supply-noise-reduction/

Guidelines for Reducing Harmonic Distortion with Decoupling Capacitors (alliedcomponents.com)

How (Not (ti.com)

In general the capacitor placed across a dual-supply amplifier configuration provide a differential mode noise improvement, as well as enabling better distortion performance by providing a more consistent source of current at the power supplies.

While I was unable to find a good, single source which directly describes the benefit to this capacitor use, I did observe supporting documentation for having capacitors to GND off of either supply rail. This dual-supply differential capacitor is certainly something considered and promoted, but the core reason may require a check-in with our designers.

If it is alright with you, we will update this thread once we learn from our design team.

Best,

Alec

0 Narek over 1 year ago in reply to Alec Saebeler

Prodigy 235 points

Hi Alec,

Thank you for the info. Please let me know if you've learned anything new from your design team.

Thanks,

Narek

0 Alec Saebeler over 1 year ago in reply to Narek

TI__Mastermind 24529 points

Hello Narek,

I expect to hear back from them next week.

Best,

Alec

+1 Alec Saebeler over 1 year ago in reply to Alec Saebeler

TI__Mastermind 24529 points

Hello Narek,

There are a few ideas here about how HD2 improvement is possible with additional de-coupling across supplies. The load current is drawn differentially from supplies instead of single-endedly. Due to supply PCB layout non-idealities, the single-ended capacitor from each supply to GND does not provide the same HD2 cancellation.

At higher frequencies the more 'immediately available' load current is provided through the differential capacitor, which will help to cancel out HD2. At lower frequencies this effect is less important as the load current need can be handled by the farther away main supplies.

Essentially, when operating at higher frequencies and need decent load current, these caps can help improve HD2.

Best,

Alec

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LMH6703: Bypass capacitor between ±Vs supplies