CS47L35 datasheet(65/300 Pages) CIRRUS

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DS1085F3

CS47L35

4.3 Digital Core

4.3.10 Noise Generator

The CS47L35 incorporates a white-noise generator that can be routed within the digital core. The main purpose of the

noise generator is to provide comfort noise in cases where silence (digital mute) is not desirable.

Figure 4-23. Digital-Core Noise Generator

The noise generator can be selected as input to any of the digital mixers or signal-processing functions within the CS47L35

digital core. The hexadecimal number (0x0D) in Fig. 4-23 indicates the corresponding x_SRCn setting for selection of the

noise generator as an input to another digital-core function.

The sample rate for the noise generator is configured using the NOISE_GEN_RATE field. See Table 4-21. Note that

sample-rate conversion is required when routing the noise generator output to any signal chain that is configured for a

different sample rate.

The noise generator is enabled by setting NOISE_GEN_ENA, described in Table 4-18. The signal level is configured using

NOISE_GEN_GAIN.

SYSCLK must be present and enabled before setting NOISE_GEN_ENA. The noise generator should be kept disabled

(NOISE_GEN_ENA = 0) if SYSCLK is not enabled. See Section 4.16.4 for further details (including requirements for

reconfiguring SYSCLK while digital core functions are enabled).

R34 (0x0022)

Tone_Generator_3

7:0 TONE1_

LVL[7:0]

0x00 Tone Generator 1 DC output level

TONE1_LVL[23:8] is coded as 2’s complement. Bits [23:20] contain the integer portion; bits

[19:0] contain the fractional portion.

The digital core 0 dBFS level corresponds to 0x10_0000 (+1) or 0xF0_0000 (–1).

R35 (0x0023)

Tone_Generator_4

15:0 TONE2_

LVL[23:8]

0x1000 Tone Generator 2 DC output level

TONE2_LVL[23:8] is coded as 2’s complement. Bits [23:20] contain the integer portion; bits

[19:0] contain the fractional portion.

The digital core 0 dBFS level corresponds to 0x10_0000 (+1) or 0xF0_0000 (–1).

R36 (0x0024)

Tone_Generator_5

7:0 TONE2_

LVL[7:0]

0x00 Tone Generator 2 DC output level

TONE2_LVL[23:8] is coded as 2’s complement. Bits [23:20] contain the integer portion; bits

[19:0] contain the fractional portion.

The digital core 0 dBFS level corresponds to 0x10_0000 (+1) or 0xF0_0000 (–1).

Table 4-18. Noise Generator Control

Bit

Label

Default

Description

R160 (0x00A0)

Comfort_Noise_

Generator

NOISE_GEN_

ENA

Noise Generator Enable

0 = Disabled

1 = Enabled

4:0

NOISE_GEN_

GAIN[4:0]

0x00

Noise generator signal level

0x00 = –114 dBFS

0x01 = –108 dBFS

0x02 = –102 dBFS

…(6-dB steps)

0x11 = –6 dBFS

0x12 = 0 dBFS

All other codes are reserved

Table 4-17. Tone Generator Control (Cont.)

Label

Default

Description

Noise Generator (0x0D)

White Noise

Generator

NOISE_GEN_ENA

NOISE_GEN_GAIN

NOISE_GEN_RATE

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