WM8281ECSSLASHR datasheet(374/392 Pages) CIRRUS

374 / 392 page

WM8281

374

Rev 4.0

MICROPHONE BIAS CIRCUIT

The WM8281 is designed to interface easily with up to 6 analogue or 8 digital microphones.

Each microphone requires a bias current (electret condenser microphones) or voltage supply (silicon

microphones); these can be provided by the MICBIAS1, MICBIAS2 or MICBIAS3 regulators on the

WM8281.

Note that the MICVDD pin can also be used (instead of MICBIASn) as a reference or power supply for

external microphones. The MICBIAS outputs are recommended, as these offer better noise

performance and independent enable/disable control.

Analogue microphones may be connected in single-ended or differential configurations, as illustrated

in Figure 84. The differential configuration provides better performance due to its rejection of

common-mode noise; the single-ended method provides a reduction in external component count.

A bias resistor is required when using an electret condenser microphone (ECM). The bias resistor

should be chosen according to the minimum operating impedance of the microphone and MICBIAS

voltage so that the maximum bias current of the WM8281 is not exceeded.

A 2.2k

 bias resistor is recommended; this provides compatibility with a wide range of microphone

components.

To ADC

PGA

VMID

IN1xN,

IN2xN,

IN3xN

IN1xP,

IN2xP,

IN3xP

MIC

GND

MICBIAS

To ADC

PGA

VMID

IN1xN,

IN2xN,

IN3xN

IN1xP,

IN2xP,

IN3xP

MIC

GND

MICBIAS

Figure 84 Single-Ended and Differential Analogue Microphone Connections

Analogue MEMS microphones can be connected to the WM8281 as illustrated in Figure 85. In this

configuration, the MICBIAS generators provide a low-noise supply for the microphones; a bias resistor

is not required.

To ADC

PGA

VREF

IN1xN,

IN2xN,

IN3xN

IN1xP,

IN2xP,

IN3xP

MEMS

Mic

MICBIAS

VDD

OUT

GND

To ADC

PGA

VREF

IN1xN,

IN2xN,

IN3xN

IN1xP,

IN2xP,

IN3xP

MEMS

Mic

MICBIAS

VDD

OUT-P

GND

OUT-N

Figure 85 Single-Ended and Differential Analogue Microphone Connections

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