CS47L85 datasheet(165/370 Pages) CIRRUS

165 / 370 page

CS47L85

Rev 4.3

165

AMBIENT NOISE CANCELLATION

The Cirrus Logic Ambient Noise Cancellation (ANC) processor within the CS47L85 provides the capability to improve the

intelligibility of a voice call by using destructive interference to reduce the acoustic energy of the ambient sound. The mono

ANC capability supports a wide variety of headset/handset applications.

The ANC processor is configured using parameters that are determined during product development and downloaded to the

CS47L85. The configuration settings are specific to the acoustic properties of the target application. The primary acoustic

elements in an application are typically the microphones and the speaker, but other components such as the plastics and

the PCBs also have significant importance to the acoustic coefficient data.

Note that the ANC configuration parameters are application-specific, and must be recalculated following any change in the

design of the acoustic elements of that application. Any mismatch between the acoustic coefficient data and the target

application will give inferior ANC performance.

The ANC processor employs digital circuits to process the ambient noise (microphone) input signal; the noise input path

(analogue or digital) is selected as described in Table 6. The selected source is filtered and processed in accordance with

the acoustic parameters programmed into the CS47L85. The resulting noise cancellation signal can be mixed with the output

signal paths using the register bits described in Table 73.

The ANC processor is responsive to variable ambient-noise conditions. Automatic gain adjustment is incorporated to support

different handset positions. Dynamic limiter and noise-gate functions are provided, to ensure best performance across a

wide range of operating conditions.

Note that the ANC configuration data is lost whenever the DCVDD power domain is removed; the ANC configuration data

must be downloaded to the CS47L85 each time the device is powered up.

The procedure for configuring the CS47L85 ANC functions is tailored to

each customer’s application; please contact your

local Cirrus Logic representative for more details.

CS47L85 Datasheet(PDF) 165 Page - Cirrus Logic