Problem with THD+N in PCM4202

Daniel Vazquez1

Other Parts Discussed in Thread: PCM4202

I am using the ADC PCM4202 and I have a problem with the THD+N:

THD +N rise up at high level of input signal. See the next figure (Blue: THD+N; Red: Input level):

I can’t get the -105 dB of THD+N that specifies datasheet.

My board has every decoupling capacitors like demo board although my input analog circuit is different from the demo board. See next figure:

The ADC is setting in slave mode, HPFD disable, dual rate with clock auto-detection and fSCKI = 256 fs, fs= 96 Khz.

How could I improve the THD+N in this conditions? Thanks very much.

over 9 years ago

0 Don Dapkus over 9 years ago

TI__Guru**** 189399 points

Hi, Daniel,

I have asked my colleague to comment on your post.

-d2

0 Justin Bohr over 9 years ago in reply to Don Dapkus

TI__Mastermind 27850 points

Hi Daniel,

I will be looking into this today and I hope to get beck with you early this week.

Justin

0 Justin Bohr over 9 years ago in reply to Justin Bohr

TI__Mastermind 27850 points

Hi Daniel,

Poor capacitors are a common cause for increased THD (Y5V is generally not recommended), another could be the voltage rating of the capacitors. We usually recommend twice the voltage you expect the capacitor to experience. Jitter in crystals can also be a source of THD or any other source on non-linearities.

Have you also seen this result using the EVM?

Justin

0 Daniel Vazquez1 over 9 years ago in reply to Justin Bohr

Prodigy 60 points

Hi Justin,

We have used capacitor with at least twice the voltage. I have obtained these results in our board.

We have obtained the same effect In three prototypes. I think this problem is caused by some capacitor, but I do not know points may be more sensitive to THD in the ADC. I'll try to change the capacitors.

Thanks.

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Problem with THD+N in PCM4202