WM8944BECSSLASHR datasheet(23/165 Pages) CIRRUS

23 / 165 page

WM8944B

Rev 4.3

INPUT PGA CONFIGURATION

Microphone and Line level audio inputs can be connected to the WM8944B in single-ended or

differential configurations. (These two configurations are illustrated in Figure 55 and Figure 56 in the

section describing the external components requirements - s

ee “Applications Information”.)

For single-ended microphone inputs, the microphone signal is connected to the non-inverting input of

the PGA (IN1/DMICDAT), whilst the inverting input of the PGA is connected to VMID. For differential

microphone inputs, the non-inverted microphone signal is connected to the non-inverting input of the

PGA (IN1/DMICDAT)

, whilst the inverted (or ‘noisy ground’) signal is connected to the inverting input

pin (AUX).

Line level inputs are connected in the same way as a single-ended microphone signal.

The non-inverting input of the PGA (IN1/DMICDAT) is configured using the P_INPGA_SEL register

bit. This register allows the selection of the two possible input pins to the PGA. The inverting input is

configured using the AUX_TO_N_INPGA register bit. The registers for configuring the Input PGA are

described in Table 2.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R39 (27h)

Input ctrl

AUX_TO_N_INP

Input PGA Inverting Input Select

0 = Connected to VMID

1 = Connected to AUX

1:0

P_INPGA_SEL

[1:0]

Input PGA Non-Inverting Input

Select

00 = Reserved

01 = Connected to IN1/DMICDAT

10 = Connected to AUX

11 = Reserved

Table 2 Input PGA Configuration

MICROPHONE BIAS CONTROL

The WM8944B 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

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