WM8994 datasheet(175/359 Pages) WOLFSON

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Production Data

WM8994

PD, April 2012, Rev 4.4

175

AIF1 - COMPANDING

The WM8994 supports A-law and

-law companding on both transmit (ADC) and receive (DAC) sides

of AIF1. This is configured using the register bits described in Table 92.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R769 (0301h)

AIF1 Control

(2)

AIF1DAC_C

OMP

AIF1 Receive Companding Enable

0 = Disabled

1 = Enabled

AIF1DAC_C

OMPMODE

AIF1 Receive Companding Type

0 = µ-law

1 = A-law

AIF1ADC_C

OMP

AIF1 Transmit Companding Enable

0 = Disabled

1 = Enabled

AIF1ADC_C

OMPMODE

AIF1 Transmit Companding Type

0 = µ-law

1 = A-law

Table 92 AIF1 Companding

Companding involves using a piecewise linear approximation of the following equations (as set out by

ITU-T G.711 standard) for data compression:

-law (where =255 for the U.S. and Japan):

F(x) = ln( 1 +

|x|) / ln( 1 + )

} for -1 ≤ x ≤ 1

A-law (where A=87.6 for Europe):

F(x) = A|x| / ( 1 + lnA)

 for x ≤ 1/A

F(x) = ( 1 + lnA|x|) / (1 + lnA)

 for 1/A ≤ x ≤ 1

The companded data is also inverted as recommended by the G.711 standard (all 8 bits are inverted

for

-law, all even data bits are inverted for A-law). The data will be transmitted as the first 8 MSBs of

data.

Companding converts 13 bits (

-law) or 12 bits (A-law) to 8 bits using non-linear quantization. This

provides greater precision for low amplitude signals than for high amplitude signals, resulting in a

greater usable dynamic range than 8 bit linear quantization. The companded signal is an 8-bit word

comprising sign (1 bit), exponent (3 bits) and mantissa (4 bits).

AIF1 8-bit mode is selected whenever AIF1DAC_COMP=1 or AIF1ADC_COMP=1. The use of 8-bit

data allows samples to be passed using as few as 8 BCLK1 cycles per LRCLK1 frame. When using

DSP mode B, 8-bit data words may be transferred consecutively every 8 BCLK1 cycles.

AIF1 8-bit mode (without Companding) may be enabled by setting AIF1DAC_COMPMODE=1 or

AIF1ADC_COMPMODE=1, when AIF1DAC_COMP=0 and AIF1ADC_COMP=0.

BIT7

BIT[6:4]

BIT[3:0]

SIGN

EXPONENT

MANTISSA

Table 93 8-bit Companded Word Composition

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