WM8962B datasheet(39/295 Pages) WOLFSON

39 / 295 page

WM8962

Rev 4.3

MICROPHONE BIAS CONTROL

There is one MICBIAS generator which provides low noise reference voltages suitable for biasing

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

Note that an external decoupling capacitor is required on the MICBIAS output. A suitable capacitor

must be connected whenever the MICBIAS output is enabled. Additional filtering of the MICBIAS

output, to reduce noise and interference, may be implemented as described in the

“Applications

Information

” section, if required.

The MICBIAS voltage can be enabled using the MICBIAS_ENA control bit; the voltage of each can be

selected using the MICBIAS_LVL register bit as detailed in Table 2.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R25 (19h)

Pwr Mgmt

(1)

MICBIAS_ENA

Microphone Bias Enable

0 = OFF (high impedance output)

1 = ON

R48 (30h)

MICBIAS

MICBIAS_LVL

Microphone Bias Voltage Control

0 = 5/6 x AVDD (approx.)

1 = 7/6 x AVDD (approx.)

Table 2 Microphone Bias Control

Note that the maximum source current capability for MICBIAS is 2.0mA. The external biasing

resistance must be large enough to limit the MICBIAS current to 2.0mA across the full microphone

impedance range.

Note that the MICVDD supply voltage must be at least 300mV higher than the desired MICBIAS

output voltage. In applications where AVDD = 1.8V, then the MICBIAS_LVL = 1 option can only be

supported if MICVDD is greater than 2.4V.

MICBIAS CURRENT DETECT

A MICBIAS Current Detect function is provided for external accessory detection. This is provided in

order to detect the insertion/removal of a microphone or the pressing/releasing of the microphone

‘hook’ switch; these events will cause a significant change in MICBIAS current flow, which can be

detected and used to generate a signal to the host processor.

The MICBIAS current detect function is enabled by setting the MICDET_ENA register bit. When this

function is enabled, two current thresholds can be defined, using the MICDET_THR and

MICSHORT_THR registers. When a change in MICBIAS current which crosses either threshold is

detected, then an interrupt event can be generated. In a typical application, accessory insertion would

be detected when the MICBIAS current exceeds MICDET_THR, and microphone hookswitch

operation would be detected when the MICBIAS current exceeds MICSHORT_THR.

The current detect threshold functions are both inputs to the Interrupt control circuit and can be used

to trigger an Interrupt event when either threshold is crossed. Both events can also be indicated as an

output on a GPIO pin -

see “General Purpose Input/Output (GPIO)”. The status flags MICDET_STS or

MICSHORT_STS are also asserted whenever the relevant current threshold is exceeded.

The current detect thresholds are enabled and controlled using the registers described in Table 3

Performance parameters for this circuit block can be found in the “Electrical Characteristics” section.

Filtering is also provided in both current detect circuits to improve reliability in conditions where AC

current spikes are present due to ambient noise conditions. This feature is described in the following

section. Further guidance on the usage of the MICBIAS current monitoring features is also described

in the following pages.

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