LM4935 datasheet(33/112 Pages) NSC

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12.0 Status & Control Registers (Continued)

12.12 AGC_1 CONFIGURATION REGISTER

This register is used to control the LM4935’s Automatic Gain Control. (Note 16)

TABLE 13. AGC_1 (0x08h)

Bits

Field

Description

AGC_ENABLE

If set the AGC controls the analog microphone preamplifier gain into the system. The microphone

input must be passed to the ADC.

3:1

AGC_TARGET

Programs the target level of the AGC. This will depend on the expected transients and desired

headroom. Refer to AGC_TIGHT (bit 7 of 0x09h) for more detail.

AGC_TARGET

Target Level

000

−6 dB

001

−8 dB

010

−10 dB

011

−12 dB

100

−14 dB

101

−16 dB

110

−18 dB

111

−20 dB

NOISE_GATE_ON

If set, signals below the noise gate threshold are muted.The noise gate is only activated after a set

period of signal absence.

7:5

NOISE_

GATE_

THRES

This field sets the expected background noise level relative to the peak signal level. The sole

presence of signals below this level will not result in an AGC gain change of the input and will be

gated from the ADC output if the NOISE_GATE_ON is set. This level must be set even if the noise

gate is not in use as it is required by the AGC algorithm.

NOISE_GATE_THRES

Level

000

−72 dB

001

−66 dB

010

−60 dB

011

−54 dB

100

−48 dB

101

−42 dB

110

−36 dB

111

−30 dB

Note 16: See the AGC overview.

LM4935 Datasheet(PDF) 33 Page - National Semiconductor (TI)

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