WM8904ECSSLASHR datasheet(39/188 Pages) WOLFSON

39 / 188 page

Pre-Production

WM8904

PP, Rev 3.3, September 2012

DIFFERENTIAL MICROPHONE INPUT

The Differential Mic PGA configuration is illustrated in Figure 23 for the Left channel. The available

gain in this mode is from +12dB to +30dB in 3dB linear steps. The input to the ADC is in phase with

the input pin selected by L_IP_SEL_N. The input to the ADC is phase inverted with respect to the

input pin selected by L_IP_SEL_P.

Note that the inverting input pin is selected using L_IP_SEL_P and the non-inverting input pin is

selected using L_IP_SEL_N. This is not the same as for the Differential Line mode.

The equivalent configuration is also available on the Right channel; this can be selected

independently of the Left channel mode.

Figure 23 Differential Microphone Mode

INPUT PGA GAIN CONTROL

The volume control gain for the Left and Right channels be independently controlled using the

LIN_VOL and RIN_VOL register fields as described in Table 3. The available gain range varies

according to the selected PGA Mode as detailed in Table 4. Note that the value ‘00000’ must not be

used in Differential Mic Mode, as the PGA will not function correctly under this setting. In single-

ended mode (L_MODE / R_MODE = 00b), the conversion from single-ended to differential within the

WM8904 adds a further 6dB of gain to the signal path.

Each input channel can be independently muted using LINMUTE and RINMUTE.

It is recommended to not adjust the gain dynamically whilst the signal path is enabled; the signal

should be muted at the input or output stage prior to adjusting the volume control.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R44 (2Ch)

Analogue Left

Input 0

LINMUTE

Left Input PGA Mute

0 = not muted

1 = muted

4:0

LIN_VOL [4:0]

00101

Left Input PGA Volume

(See Table 4 for volume range)

R45 (2Dh)

Analogue

Right Input 0

RINMUTE

Right Input PGA Mute

0 = not muted

1 = muted

4:0

RIN_VOL [4:0]

00101

Right Input PGA Volume

(See Table 4 for volume range)

Table 3 Input PGA Volume Control

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