PCM4108CPAPT datasheet(24/39 Pages) TI

24 / 39 page

PCM4108

SBAS354 − JUNE 2005

www.ti.com

STANDALONE MODE CONFIGURATION

Standalone mode is selected by forcing the MODE input

(pin 12) low. Standalone mode operation provides a

subset of the functions available in Software mode, while

providing an option for a simplified control model.

Standalone configuration is accomplished by either

hardwiring or driving a small set of input pins with external

logic or switches. Standalone mode functions include

sampling mode and audio data format selection, an

all-channel soft mute function, and digital de-emphasis

filtering. The following paragraphs provide a brief

description of each function available when using

Standalone mode.

Sampling Mode

The sampling mode is selected using the FS0 (pin 36) and

FS1 (pin 37) inputs. A more detailed discussion of the

sampling modes was provided in an earlier section of this

data sheet. Table 2 summarizes the sampling mode

configuration for Standalone mode.

Table 2. Sampling Mode Configuration

FS1

FS0

SAMPLING MODE

Single Rate

Dual Rate

Quad Rate

− Not Used −

Audio Data Format

The audio data format is selected using the FMT0 (pin 33),

FMT1 (pin 34), and FMT2 (pin 35) inputs. A detailed

discussion of the audio serial port operation and the

corresponding data formats was provided in the Audio

Serial Port section on pages 20 through 23. For

Standalone mode, the LRCK polarity is always normal,

while the serial audio data is always sampled on the rising

edge of the BCK clock. Table 3 shows the audio data

format configuration for Standalone mode.

Table 3. Audio Data Format Configuration

FMT2

FMT1

FMT0

AUDIO DATA FORMAT

24-bit, left-justified

24-bit I2S

TDM with zero BCK delay

TDM with one BCK delay

24-bit, right-justified

20-bit, right-justified

18-bit, right-justified

16-bit, right-justified

Soft Mute Function

The MUTE input (pin 14) may be used in either the

Standalone or Software modes to simultaneously mute the

eight output channels. The soft mute function slowly ramps

the digital output attenuation from its current setting to the

mute level, minimizing or eliminating audible artifacts.

Table 4 summarizes MUTE function operation.

Table 4. Mute Function Configuration

MUTE

ANALOG OUTPUTS

On (mute disabled)

Muted

Digital De-Emphasis

This is a global digital function (common to all eight

channels) and provides de-emphasis of the higher

frequency

content

within

the

20kHz

audio

band.

De-emphasis is required when the input audio data has

been pre-emphasized. Pre-emphasis entails increasing

the amplitude of the higher frequency components in the

20kHz audio band using a standardized filter function in

order to enhance the high-frequency response. The

PCM4108 de-emphasis filters implement the standard

50/15

µs de-emphasis transfer function commonly used in

digital audio applications.

De-emphasis filtering is available for three input sampling

frequencies in Single Rate sampling mode: 32kHz,

44.1kHz, and 48kHz. De-emphasis is not available when

operating in Dual or Quad Rate sampling modes. The

de-emphasis filter is selected using the DEM0 (pin 16) and

DEM1 (pin 15) inputs. Table 5 illustrates the de-emphasis

filter configuration for Standalone mode.

Table 5. Digital De-Emphasis Configuration

DEM1

DEM0

DIGITAL DE-EMPHASIS MODE

Off (de-emphasis disabled)

48kHz

44.1kHz

32kHz

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