R261 datasheet(14/28 Pages) ONSEMI

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BelaSigna R261

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Microphone Placement & Selection

The flexibility of the BelaSigna R261 ROM−based noise

reduction algorithm offers a variety of possible microphone

placements, but the default algorithm will operate optimally

when the microphones are placed in the following

configuration:

• The two microphones are facing the user’s mouth

• The microphone centers are located within 10 to 25 mm

from each other

As mentioned, other configurations that differ from the

above guidelines can be supported through the use of the

custom mode, as described earlier.

BelaSigna R261 does not require any acoustic

microphone calibration procedure.

The selection of the microphones should be made in

cooperation with ON Semiconductor, such as the built−in

algorithm can operate seamlessly. The following guidelines

can be used for a pre−selection:

• Two omni−directional microphones with similar

characteristics should be used

• The microphone sensitivity should be −42 dB (where

0 dB = 1 V/Pa, at 1 kHz)

• The microphones are two terminal microphones

• The microphone power supply is either 1 V, or 2 V if it

has to be provided by BelaSigna R261

• The dynamic range of BelaSigna R261 on its analog

input channels is 2.0 V peak−to−peak, after

amplification by the default gain value of 30 dB using

BelaSigna R261’s input preamplifiers

• When higher sensitivity microphones have to be used,

the preamp gain will be adjustable to match the 2.0 Vpp

input voltage swing on BelaSigna R261, but this will

require a custom tuning operation, as described later.

Operating Modes

The default application in ROM on BelaSigna R261 has

five Operating Modes. The Operating Modes are

summarized in Table 7.

Table 7. OPERATING MODES SUMMARY

Operating

Mode

Switching

Description

Active

Active mode is the default operating mode. The

chip normally enters Active mode upon boot−up

and when exiting Sleep mode. Active mode can

also be entered via I2C from another mode.

In Active mode, the two−microphone noise reduction algorithm is

executed on the audio inputs and both the processed and unpro-

cessed signals are sent to the audio outputs.

Bypass

Bypass mode can only be entered via an I2C

command.

In Bypass mode, no signal processing is done on the audio in-

puts. The inputs are passed directly to the audio outputs.

While in Bypass mode, BelaSigna R261 collects statistics on the

input signals that can be retrieved via I2C. These signal statistics

can be used for level calibration and other debugging. For more

information using Bypass mode for calibration and debugging see

the “BelaSigna R261 Configuration and Communications Guide”

Line−Out

Line−Out mode can only be entered via an I2C

command.

In Line−Out mode, no signal processing or digital processing of

the audio inputs is done. The analog signals from the input stage

preamplifiers are routed back via the lineout pins (LOUT0 and

LOUT1). When in this mode, BelaSigna R261 runs off an internal

clock source, thereby allowing the external clock to be disabled.

Note that LOUT1 is not available on the 26−ball WLCSP package.

Sleep

Sleep mode can be entered via I2C commands or

by using the SLEEP_CTRL pin.

When Sleep mode is entered via I2C, the chip will

exit Sleep mode only based on activity on the

I2C_SCL pin.

When put to Sleep mode via the SLEEP_CTRL

pin, the chip will exit Sleep mode only when the

SLEEP_CTRL pin is toggled again.

Sleep mode will be automatically entered if

BelaSigna R261 detects that a required external

clock is no longer present. For more information,

see the Sleep Control section below.

In Sleep mode no signal processing is done. All analog blocks of

the chip are disabled and the digital core continues to run off an

internal low−speed oscillator, thereby allowing the external clock

to be disabled when the chip is asleep.

This is BelaSigna R261’s lowest power operating mode.

Stand−By

Stand−By mode is an intermediate mode that is

only used when exiting sleep mode by an I2C

command.

When I2C is used to exit Sleep mode, the application will trans-

ition to Stand−By mode, and will wait until the master I2C device

issues a Switch_Mode command to enter another processing

mode like Active, Bypass or Line−Out.

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