CS47L85 datasheet(49/370 Pages) CIRRUS

49 / 370 page

CS47L85

Rev 4.3

ANALOGUE MICROPHONE INPUT

Up to nine analogue microphones can be connected to the CS47L85, either in single-ended or differential mode. The

applicable mode, and input pin selection, is controlled using the INnx_SRC registers, as described later.

The CS47L85 includes external accessory detection circuits, which can detect the presence of a microphone, and the status

of a hookswitch or other push-buttons. When using this function, it is recommended to use the IN1B or IN2B analogue

microphone input paths, to ensure best immunity to electrical transients arising from the push-buttons.

For single-ended input, the microphone signal is connected to the non-inverting input of the PGAs (INnLP or INnRP). The

inverting inputs of the PGAs are connected to an internal reference in this configuration.

For differential input, the non-inverted microphone signal is connected to the non-inverting input of the PGAs (INnLP or

INnRP

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

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

analogue input paths is fixed across all PGA gain settings.

The Electret Condenser Microphone (ECM) analogue input configurations are illustrated in Figure 14 and Figure 15. The

integrated MICBIAS generators provide a low noise reference for biasing the ECMs.

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 14 Single-Ended ECM Input

Figure 15 Differential ECM Input

Analogue MEMS microphones can be connected to the CS47L85 in a similar manner to the ECM configurations described

above; typical configurations are illustrated in Figure 16 and Figure 17. In this configuration, the integrated MICBIAS

generators provide a low-noise power supply for the microphones.

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 16 Single-Ended MEMS Input

Figure 17 Differential MEMS Input

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.

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