OPA2322 THD and Noise Issue

Samuel Jaffe

Other Parts Discussed in Thread: OPA2322, OPA1602, OPA1662, OPA1652, OPA1642

Hi E2E,

I have a customer who's using our OPA2322 for an audio design. He has a simple gain stage design and he's getting a noise curve much like Figure 18 in the datasheet:

Notice the upturn in THD and Noise at the 1kHz mark. For audio applications we'd really want that at 20+kHz. I assume, since it's in the datasheet, that this is expected behavior. We were wondering:

1. What about this op amp is causing this to happen?

2. Would this be improved by using a different type of op amp? CMOS vs BJT for instance.

3. Do we have other MSOP-8 op amps that have better distortion performance in the audio band?

Thanks!

-Sam

over 7 years ago

0 Tim Claycomb over 7 years ago

TI__Genius 15410 points

Hi Samuel,

The reason the THD+N curve increases at high frequency is because the amplifiers loop gain is decreasing. I recommend reading the blog "Amp up your cans: Test your headphone amplifier distortion knowledge (Part 3)" for more information on this.

For better THD+N performance in the audio band, I recommend taking a look at our SoundPlus™ audio amplifiers (OPA16xx), such as the OPA1602, OPA1642, OPA1652, OPA1662.

-Tim Claycomb

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

TI__Mastermind 25590 points

Tim,

Thanks for this great info! We played around with the circuit and it turns out the culprit was a capacitor. It had Barium Titanate which adds a voltage coefficient to the capacitance which gave us this undesired characteristic.

Here are a few articles on it written by our very own John Caldwell!

http://www.edn.com/design/analog/4416466/Signal-distortion-from-high-K-ceramic-capacitors

http://www.edn.com/design/analog/4426318/More-about-understanding-the-distortion-mechanism-of-high-K-MLCCs

Fascinating stuff! Thanks again!

-Sam

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OPA2322 THD and Noise Issue