WM8945ECSSLASHR datasheet(25/169 Pages) WOLFSON

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Production Data

WM8945

PD, May 2011, Rev 4.1

MICROPHONE BIAS CONTROL

The WM8945 provides a low noise reference voltage suitable for biasing electret condenser (ECM)

type microphones via an external resistor. Refer to the “Applications Information” section for

recommended components. The MICBIAS voltage is enabled using the MICB_ENA register bit; the

voltage can be selected using the MICB_LVL bit, as described in Table 3.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R2 (02h)

Power

Management 1

MICB_ENA

Microphone Bias Enable

0 = Disabled

1 = Enabled

R39 (27h)

Input Ctrl

MICB_LVL

Microphone Bias Voltage control

0 = 0.9 x LDOVOUT

1 = 0.65 x LDOVOUT

Table 3 Microphone Bias Control

INPUT PGA GAIN CONTROL

The volume control gain for the PGA is adjusted using the PGAL_VOL register field as described in

Table 4. The gain range is -12dB to +35.25dB in 0.75dB steps. The gains on the inverting and non-

inverting inputs to the PGA are always equal. The input PGA can be muted using the PGAL_MUTE

mute bit.

The PGA_VU bit controls the loading of digital volume control data. The PGAL_VOL control data is

only loaded into the respective control register when PGA_VU = 1.

To prevent “zipper noise”, a zero-cross function is provided on the input PGA. When this feature is

enabled, volume updates will not take place until a zero-crossing is detected. In the case of a long

period without zero-crossings, a timeout function is provided. When the zero-cross function is

enabled, the volume will update after the timeout period if no earlier zero-cross has occurred. The

timeout clock is enabled using TOCLK_ENA. See “Clocking and Sample Rates” for the definition of

this bit. Note that the zero-cross function can be supported without TOCLK enabled, but the timeout

function will not be provided in this case.

The Input PGA volume control register fields are described in Table 4.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R40 (28h)

Left INP PGA

gain ctrl

PGA_VU

Input PGA Volume Update

Writing a 1 to this bit enables the

Left PGA volume to be updated

PGAL_ZC

Left Input PGA Zero Cross Detector

0 = Change gain immediately

1 = Change gain on zero cross only

PGAL_MUTE

Left Input PGA Mute

0 = Disable Mute

1 = Enable Mute

5:0

PGAL_VOL [5:0]

01_0000

(0dB)

Left Input PGA Volume

00_0000 = -12dB

00_0001 = -11.25dB

…

01_0000 = 0dB

...

11_1111 = +35.25

(See Table 5 for volume range)

Table 4 Input PGA Volume Control

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