# Active power noise reduction feature

Usually, the 5V power rail of raspberry pi is generated from a DC/DC converter, which always means pool ripple rejection. To overcome this , the power rail of the HAT has been build with two levels of active regulation, which brings extremely good PSRR performance in full band under full load, so the power supply of the DAC would be perfectly clean.

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This processing unit is placed at the backend of the power input switch, so both RPi power and external power sources are valid.
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<figure><img src="https://389921961-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FjPowryxiQvRDiYHC9qWy%2Fuploads%2FmNL9tJ1p3u1apTBqRdg0%2Fwisdpi%20hifi%20dac%20noise%20reduction.png?alt=media&#x26;token=81ecd8d5-4598-4e31-a567-b23eabc9a5e6" alt="" width="375"><figcaption></figcaption></figure>

## Laboratory test data

When VDD in full load, PSRR = 111.61dB

<figure><img src="https://389921961-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FjPowryxiQvRDiYHC9qWy%2Fuploads%2FTNaO49Xv7t3I93pGejba%2FwisdPi%20HiFi%20DAC%20test%20data%2001.png?alt=media&#x26;token=861cfe5c-4206-4859-9635-9db02fd2082d" alt=""><figcaption></figcaption></figure>

When VDD in lite load, PSRR = 119.78dB

<figure><img src="https://389921961-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FjPowryxiQvRDiYHC9qWy%2Fuploads%2Fa2CKNx4768e6ey8iWxEj%2FwisdPi%20HiFi%20DAC%20test%20data%2002.png?alt=media&#x26;token=3789a3e9-b938-4040-acdc-d1d1f238ba89" alt=""><figcaption></figcaption></figure>

{% hint style="info" %}
The test data is from wisdPi laboratory and is for reference only.
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