LME49721: LME49721 THD+N Rises with Gain

Samuel Jaffe

Part Number: LME49721

Hi E2E,

My customer is using the LME49721 in a non-inverting configuration with resistors, caps, and a digital potentiometer in the feedback. The variable gain stage is causing the THD+N ratio to slowly rise up as it gets closer to the clip point.

If we remove the digital potentiometer and use a fixed gain, the THD+N curve looks much like the datasheet (see below)

If we remove the digital potentiometer and use a voltage follower, we see a bump before the rise.

If we use the original circuit with the digital potentiometer, this bump gets worse.

Do we have any thoughts on what might be causing this bump?

Thanks,

-Sam

over 7 years ago

0 Ivan Salazar over 7 years ago

TI__Guru** 102035 points

HI Samuel,

The LME49721 performance is obtained with the specs from the datasheet. Perhaps you could implement the amplitude/volume control as a previous stage before the LME49721 so it can have a fixed gain.

Best regards,
-Ivan Salazar
Texas Instruments

0 Samuel Jaffe over 7 years ago in reply to Ivan Salazar

TI__Mastermind 25590 points

Ivan,

That's a smart workaround. I'll suggest that to the customer.

But in terms of what's happening, do you have any ideas as to what's causing this bump?

Thanks,

-Sam

0 Samuel Jaffe over 7 years ago in reply to Samuel Jaffe

TI__Mastermind 25590 points

Thoughts?

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LME49721: LME49721 THD+N Rises with Gain