CS47L85 datasheet(350/370 Pages) CIRRUS

350 / 370 page

CS47L85

350

Rev 4.3

MICROPHONE BIAS CIRCUIT

The CS47L85 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 CS47L85.

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 88. 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 CS47L85 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 88 Single-Ended and Differential Analogue Microphone Connections

Analogue MEMS microphones can be connected to the CS47L85 as illustrated in Figure 89. 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 89 Single-Ended and Differential Analogue Microphone Connections

CS47L85 Datasheet(PDF) 350 Page - Cirrus Logic

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