WM8993 datasheet(36/229 Pages) WOLFSON

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WM8993

Production Data

PD, November 2010, Rev 4.0

MICROPHONE INPUTS

Up to four microphones can be connected to the WM8993, either in single-ended or differential

mode. A dedicated PGA is provided for each microphone input. Two low noise microphone bias

circuits are provided, reducing the need for external components.

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

PGAs (IN1LN, IN2LN, IN1RN or IN2RN). The non-inverting inputs of the PGAs are internally

connected to VMID in this configuration. The non-inverting input pins IN1LP, IN2LP, IN1RP and

IN2RP are free to be used as line connections to the input or output mixers in this configuration.

For differential microphone inputs, the non-inverted microphone signal is connected to the non-

inverting input of the PGAs (IN1LP, IN2LP, IN1RP or IN2RP), whilst the inverted (or ‘noisy ground’)

signal is connected to the inverting input pins (IN1LN, IN2LN, IN1RN and IN2RN).

The gain of the input PGAs is controlled via register settings, as defined in Table 4. Note that the

input impedance of both inverting and non-inverting inputs changes with the input PGA gain setting,

as described under “Electrical Characteristics”. See also the “Applications Information” for details of

input resistance at all PGA Gain settings.

The microphone input configurations are illustrated in Figure 8 and Figure 9. Note that any PGA input

pin that is used in either microphone configuration is not available for use as a line input path at the

same time.

MICBIAS

MIC

GND

input

mixers

PGA

Line Input

VMID

IN1LN,

IN2LN,

IN1RN,

IN2RN

IN1LP,

IN2LP,

IN1RP,

IN2RP

MIC

GND

input

mixers

PGA

VMID

MICBIAS

IN1LN,

IN2LN,

IN1RN,

IN2RN

IN1LP,

IN2LP,

IN1RP,

IN2RP

Figure 8 Single-Ended Microphone Input

Figure 9 Differential Microphone Input

MICROPHONE BIAS CONTROL

There are two MICBIAS generators which provide low noise reference voltages suitable for biasing

electret condenser (ECM) type microphones via an external resistor. Note that an external decoupling

capacitor is also required on each of the MICBIAS outputs. A suitable capacitor must be connected

whenever the associated MICBIAS output is enabled. Refer to the “Applications Information” section

for recommended external components.

The MICBIAS voltages can be enabled using the MICB1_ENA and MICB2_ENA control bits; the

voltage of each can be selected using the MICB1_LVL and MICB2_LVL register bits as detailed in

Table 1.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R1 (01h)

Power

Managem

ent (1)

MICB2_ENA

Microphone Bias 2 Enable

0 = OFF (high impedance output)

1 = ON

MICB1_ENA

Microphone Bias 1 Enable

0 = OFF (high impedance output)

1 = ON

R58 (3Ah)

MICBIAS

MICB2_LVL

Microphone Bias 2 Voltage Control

0 = 0.9 * AVDD1

1 = 0.65 * AVDD1

MICB1_LVL

Microphone Bias 1 Voltage Control

0 = 0.9 * AVDD1

1 = 0.65 * AVDD1

Table 1 Microphone Bias Control

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