CS42L92 datasheet(32/333 Pages) CIRRUS

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DS1162F2

CS42L92

4.2 Input Signal Path

4.2.1

Analog Microphone Input

Up to eight analog microphones can be connected to the CS42L92, either in single-ended or differential configuration. The

input configuration and pin selection is controlled using INnx_SRC, as described in Section 4.2.6.

The CS42L92 includes external accessory-detection circuits that can report the presence of a microphone and the status

of a hook switch or other push buttons. When using this function, it is recommended to use the IN1ALx, IN1BLx, or IN1BR

analog 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 noninverting input of the PGAs. The inverting inputs of

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

For differential input, the noninverted microphone signal is connected to the noninverting input of the PGAs and the

inverted (or noisy ground) signal is connected to the inverting input pins.

The gain of the input PGAs is controlled via register settings, as defined in Section 4.2.6. Note that the input impedance

of the analog input paths is fixed across all PGA gain settings.

The ECM analog input configurations are shown in Fig. 4-3 and Fig. 4-4. The integrated MICBIAS generators provide a

low noise reference for biasing the ECMs.

Pseudodifferential connection is also possible—this is similar to the configuration shown in Fig. 4-4, but the GND

connection is directly to the microphone (and INnxN capacitor), instead of via a resistor. The typical connections for

pseudodifferential input are shown in Fig. 4-5.

Note that pseudodifferential input is the recommended configuration if the accessory-detection functions are used on this

input path. The INnx_SRC field settings are the same for pseudodifferential connection as for differential.

The IN1ALN pin can be used as the inverting input connection for the IN1L and IN1R paths concurrently. This allows two

microphones to be supported, in pseudodifferential configuration, while minimizing the number of pin connections

required—see Fig. 4-6.

Figure 4-3. Single-Ended ECM Input

Figure 4-4. Differential ECM Input

To ADC

VREF

INnAxN,

IN1BLN

INnAxP,

INnBLP,

INnBx

ECM

GND

MICBIAS

PGA

–

To ADC

VREF

INnAxN,

IN1BLN

INnAxP,

INnBLP,

INnBx

ECM

GND

MICBIAS

PGA

–

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