WM8850 datasheet(45/223 Pages) WOLFSON

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Pre-Production

WM8850

PP, April 2011, Rev 3.2

A low-noise microphone bias generator is provided as part of Port-B, which is suitable for use as a

bias supply for analogue microphones. The control of the microphone bias level is via the Pin Widget

Control Verb.

Port-B supports impedance sensing when using the microphone bias generator; this can be read

directly from the Pin Sense Verb. Port-B also supports presence detect, using the Pin Sense Verb.

If nothing is plugged into Port-B it is possible to use an automute function which will automatically

replace the samples in the stream with zeros, thus avoiding any noise being transmitted when there is

no input device connected. This function can be enabled using the vendor-specific Auto-Mute Control

Verb.

SET VERB

BIT

BITFIELD

NAME

DEFAULT

DESCRIPTION

7B0h

PD_

AUTOMUTE

Auto-Mute Control:

0 = Automute disabled

1 = Automute enabled

Note: When PD_AUTOMUTE=1 and

Presence Detect (bit 31 in verb F09h)=1 the

WM8850 will replace the samples in the

stream with zeros

PGA2 (NID = 0Bh)

Table 12 gives a summary of the PGA2 node:

NODE SUMMARY INFORMATION

NID

0Ch

Widget Type

Audio Selector

Supported Get Verbs

Bh, F00h, F02h, FB2h

Supported Set Verbs

3h, 7B2h, 7B3h

Unsolicited Responses

None

Vendor-Specific Verbs

FB2h, 7B2h, 7B3h : PGA Control Verb

Table 12 PGA2 Node Summary Information

PGA2 provides analogue gain for the inputs to Port-B, allowing the signal level to be adjusted by up to

+/-12dB in 0.5dB steps. Gain can be applied to left and right channels independently if required.

Additionally, a mute function is available – again this can be applied to separate channels as required.

The gain of PGA2 is controlled using the Amplifier Gain/Mute Verb.

PGA2 uses an internal zero cross detect circuit to ensure that all gain changes occur while the signal

passes through the zero point. This function eliminates any potential DC steps that can occur if gain

changes are applied at other times, and therefore the potential for zipper noise is removed. If no zero

cross occurs within a specified time after the gain change is requested via a register write a timeout

period will elapse and the gain will be changed regardless. This timeout period can be changed using

the vendor-specific PGA Control Verb:

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