CS47L35 datasheet(142/300 Pages) CIRRUS

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142

DS1085F3

CS47L35

4.11 Output Signal Path

4.11.5 Output Signal Path Noise-Gate Control

The CS47L35 provides a digital noise-gate function for each of the output signal paths. The noise gate ensures best noise

performance when the signal path is idle. When the noise gate is enabled, and the applicable signal level is below the

noise-gate threshold, the noise gate is activated, causing the signal path to be muted.

The noise-gate function is enabled by setting NGATE_ENA, as described in Table 4-69.

For each output path, the noise gate may be associated with one or more of the signal path threshold detection functions

using the x_NGATE_SRC fields. When more than one signal threshold is selected, the output-path noise gate is only

activated (i.e., muted) when all of the respective signal thresholds are satisfied.

For example, if the OUT1L noise gate is associated with the OUT1L and OUT1R signal paths, the OUT1L signal path is

only muted if both the OUT1L and OUT1R signal levels are below the respective thresholds.

The noise-gate threshold (the signal level below which the noise gate is activated) is set using NGATE_THR. Note that,

for each output path, the noise-gate threshold represents the signal level at the respective output pins; the threshold is

therefore independent of the digital volume and PGA gain settings.

Note that, although there is only one noise-gate threshold level (NGATE_THR), each of the output-path noise gates may

be activated independently, according to the respective signal content and the associated threshold configurations.

To prevent erroneous triggering, a time delay is applied before the gate is activated; the noise gate is only activated (i.e.,

muted) when the output levels are below the applicable signal level thresholds for longer than the noise-gate hold time.

The hold time is set using the NGATE_HOLD field.

When the noise gate is activated, the CS47L35 gradually attenuates the respective signal path at the rate set by OUT_

VD_RAMP (see Table 4-67). When the noise gate is deactivated, the output volume increases at the rate set by OUT_VI_

RAMP.

0x24

–46.0

0x55

–21.5

0x86

3.0

0xB7

27.5

0x25

–45.5

0x56

–21.0

0x87

3.5

0xB8

28.0

0x26

–45.0

0x57

–20.5

0x88

4.0

0xB9

28.5

0x27

–44.5

0x58

–20.0

0x89

4.5

0xBA

29.0

0x28

–44.0

0x59

–19.5

0x8A

5.0

0xBB

29.5

0x29

–43.5

0x5A

–19.0

0x8B

5.5

0xBC

30.0

0x2A

–43.0

0x5B

–18.5

0x8C

6.0

0xBD

30.5

0x2B

–42.5

0x5C

–18.0

0x8D

6.5

0xBE

31.0

0x2C

–42.0

0x5D

–17.5

0x8E

7.0

0xBF

31.5

0x2D

–41.5

0x5E

–17.0

0x8F

7.5

0xC0–0xFF

Reserved

0x2E

–41.0

0x5F

–16.5

0x90

8.0

0x2F

–40.5

0x60

–16.0

0x91

8.5

0x30

–40.0

0x61

–15.5

0x92

9.0

Table 4-68. Output Signal Path Digital Volume Range (Cont.)

Output Volume

Volume (dB)

Output Volume

Volume (dB)

Output Volume

Volume (dB)

Output Volume

Volume (dB)

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