DA7218 datasheet(36/198 Pages) RENESAS

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DA7218

Ultra-Low Power Stereo Codec

Datasheet

Revision 3.4

24-Dec-2021

CFR0011-120-00

36 of 197

9.3.1.3

Automatic Level Control

For improved sound recordings of signals with a large volume range, the DA7218 offers a fully-

configurable automatic recording level control (ALC) for microphone inputs. This is enabled via the

ALC_CTRL1, and can be enabled independently on any of the four input channels. The ALC

monitors the digital signal after the ADC and adjusts the microphones’ analog and digital gain to

maintain a constant recording level, regardless of the analog input signal level.

Operation of ALC is illustrated in Figure 11. When the input signal volume is high, the ALC system

will reduce the overall gain until the output volume is below the specified maximum value. When the

input signal volume is low, the ALC will increase the gain until the output volume increases above the

specified minimum value. If the output signal is within the desired signal level (between the specified

minimum and maximum levels), the ALC does nothing.

The minimum and the maximum thresholds that trigger a gain change of the ALC are programmed

by the alc_threshold_min and alc_threshold_max controls.

ALC Input

ALC Gain

ALC Output

Release time

Attack time

Figure 11: Principle of Operation of the ALC

The ALC can operate in two modes; Digital-Only mode and Hybrid (combined analog and digital

gain) mode.

In Digital-Only mode only the digital gain in the ADC is altered. Note that although the ALC is

controlling the gain, it does not modify any of the registers in_1l_digital_gain, in_1r_digital_gain,

in_2l_digital_gain, or in_2r_digital_gain. These registers are ignored while the ALC is in operation.

The minimum and maximum levels of digital gain that can be applied by the ALC are controlled using

alc_atten_max and alc_gain_max.

When using analog microphones, Hybrid mode can be enabled using alc_sync_mode. See section

9.3.1.5 for details on ALC calibration in Hybrid mode.

In Hybrid mode, the total gain is made up of an analog gain (which is applied to the microphone

amplifiers) and a digital gain, (which is implemented in the filtering stage).The ALC block monitors

and controls the gain of the microphone and the ADC. Note that although the ALC is controlling the

gain, it does not modify any of the registers mixin_1_amp_gain or mixin_2_amp_gain, nor does it

modify any of the digital gain registers in_1l_digital_gain, in_1r_digital_gain, in_2l_digital_gain, or

in_2r_digital_gain. These registers are ignored while the ALC is in operation.

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