R262 datasheet(16/28 Pages) ONSEMI

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BelaSigna R262

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Microphone Placement & Selection

The flexibility of the BelaSigna R262 noise reduction

algorithm doesn’t restrict microphone placements, but the

default

algorithm

will

operate

optimally

with

omnidirectional microphones 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 are fully supported. For example, a 15 cm

distance between the two microphones will not degrade the

performance as long as the microphones are both facing the

user’s mouth. Alternatively, a configuration with one

microphone at the front and one microphone at the back will

not degrade the performance either, as long as the distance

between the microphones is no more than 2 cm.

BelaSigna R262 does not require any acoustic

microphone calibration procedure.

When selecting microphones to be used with BelaSigna

R262, the following guidelines should be used:

• Two omni−directional microphones with similar

characteristics should be used

• The microphone sensitivity should be approximately

−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

(recommended), or 2 V if it is to be provided by

BelaSigna R262

• The dynamic range of BelaSigna R262 on its analog

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

amplification by the default gain value of 24 dB using

BelaSigna R262’s input preamplifiers

• When higher sensitivity microphones are used, the

preamp gain should be adjusted to match the 2.0 Vpp

input voltage swing on BelaSigna R262, but this will

require special configuration of the ROM application,

as described later. As an example, using microphones

with a −22 dB sensitivity typically requires that the

preamplifier gains be changed down to 12 dB.

• When MEMS microphone are to be used, a general

increase of the algorithm performance can be expected

due to the improved self noise of these microphones,

compared to conventional electret microphones. For

applications requiring microphone configurations

differing significantly from the above recommendations,

contact your local ON Semiconductor support

representative.

Operating Modes

The default application stored in the ROM of BelaSigna

R262 has four Operating Modes. The Operating Modes are

summarized in Table 8.

Table 8. OPERATING MODES SUMMARY

Operating

Mode

Switching

Description

Active

Active mode can be entered at boot time, depend-

ing on the BOOT_SEL configuration and when

exiting Sleep mode. Active mode can also be

entered via an I2C command from another mode.

In Active mode, the noise reduction algorithm is executed. While

in Active mode, BelaSigna R262 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 in-

formation using Active mode for calibration and debugging see

the BelaSigna R262 Communications and Configuration Guide.

Bypass

Bypass mode can be entered at boot time, de-

pending on the BOOT_SEL configuration. It can

also be entered via an I2C command from another

mode.

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 R262 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 in-

formation using Bypass mode for calibration and debugging see

the BelaSigna R262 Communications and Configuration Guide.

Sleep

Sleep mode can be entered via I2C commands.

When Sleep mode is entered via I2C, the chip will

exit Sleep mode only based on activity on the

I2C_SCL pin. Sleep mode will be automatically

entered if BelaSigna R262 detects that a required

external clock is no longer present. For more in-

formation, 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 R262’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 or Bypass. If no such command is issued, Be-

laSigna R262 will return to Sleep mode and wait for a valid wake−

up sequence.

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