PCM1821-Q1: Antialias LPF from PCM1808

Youhei Miyaoka

Part Number: PCM1821-Q1
Other Parts Discussed in Thread: PCM1808, PCM1821

Hello team,

My customer think to use PCM1821 for next project. In previous project, they used PCM1808.

Seeing from datahseet, PCM1821 does not have Antialias LPF in Functional Block Diagram. However PCM1808 have it.

If they change to PCM1821 from PCM1808, does external Antialias LPF needed? If it depends on some criteria, please also teach me it.

Regards,

Youhei MIYOKA

3 months ago

0 Daveon Douglas 3 months ago

TI__Mastermind 28240 points

Hi,

While not explicitly stated in the d/s there should be a integrated anti-aliasing filter within the ADC. I will confirm and update this thread.

0 Youhei Miyaoka 2 months ago in reply to Daveon Douglas

TI__Expert 4885 points

Hi Daveon,

Thanks. Looking forward to your feedbacks!

Regards,

Youhei MIYAOKA

0 Daveon Douglas 2 months ago in reply to Youhei Miyaoka

TI__Mastermind 28240 points

Hi,

Will update thread early next week, pending feedback from design

0 Youhei Miyaoka 2 months ago in reply to Daveon Douglas

TI__Expert 4885 points

Hello Daveon,

Is there any feedback from design team?

Regards,

Youhei

0 Garret Godfrey 2 months ago in reply to Youhei Miyaoka

TI__Genius 9005 points

Hi Youhei,

Daveon is out of office for the rest of the week and can return with his feedback next week.

Best,

Garret

0 Youhei Miyaoka 2 months ago in reply to Garret Godfrey

TI__Expert 4885 points

Hello Daveon,

Can you update this topic please?

Regards,

Youhei

0 Jeff McPherson 2 months ago in reply to Youhei Miyaoka

TI__Mastermind 49260 points

Hi Miyaoka-san,

Sorry for the delay. I do not have the update from design, but I do know that PCM182x does not generally require an anti-aliasing filter. The sigma delta architecture takes care of it on its own.

There is an edge case where if the out of band noise (>20kHz) is significantly high (>60dBFS) then an anti-aliasing filter is needed otherwise the ADC becomes saturated. However in most applications this does not happen. It would only be a concern if the input source is known to have high frequency / switching characteristics. 99% of the time this is not an issue.

Best regards,
Jeff McPherson

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PCM1821-Q1: Antialias LPF from PCM1808