Delta MS210 User Manual download pdf (Page 20)

MS210

MS210 DS004 www.mshinetek.com

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The above information is the exclusive intellectual property of M-Shine Technologies Corporation and shall not be disclosed, distributed without permission

rom M-

hine.

SPI Power Noise Rejection

When recording, SPI flash always generates large noise on power signals. This is because the internal

charge-pump will be enabled when erasing the sector before record sound information to it, and

programming the flash will also use more power than idle states. When recording, sound information is

record in “pages”, and generates noise around 32 Hz. The noise is annoying and need to be filtered clearly.

Small noise in MBIAS will be amplified by OP-AMP and be recorded.

Instead of regulated VAG and MBIAS signal, MS210 uses “dynamic” method to reduce the power noise as

the following figure.

AVDD

Figure 13. Power Noise Rejection Figure

If AVDD has an additive noise N(t), VAG will have noise N(t)*R

Also, because MBIAS has also the noise from AVDD, and VMIC has noise N’(t). If R

>>R

, VAA will have

signal as follow:

)()(

tNtNVAA

•

⎟

⎠

⎞

⎜

⎝

⎛

•−

′

Eq. 1

ADC result will be VAA-VAG, which is the following equation:

Assume the power noise is low frequency that C5 has no effect.

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