wm8400 Wolfson Microelectronics plc, wm8400 Datasheet - Page 129

• Manufacturer Part Number: wm8400
• Description: Wolfson Audioplustm Hi-fi Audio Codec And Power Management Unit For Mobile Multimedia
• Manufacturer: Wolfson Microelectronics plc

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Pre-Production
COMPANDING
The WM8400 supports A-law and µ-law companding on both transmit (ADC) and receive (DAC)
sides as shown in Table 74.
Table 74 Companding Control
Companding involves using a piecewise linear approximation of the following equations (as set out
by ITU-T G.711 standard) for data compression:
µ-law (where µ=255 for the U.S. and Japan):
F(x) = ln( 1 + µ|x|) / ln( 1 + µ)
A-law (where A=87.6 for Europe):
F(x) = A|x| / ( 1 + lnA)
F(x) = ( 1 + lnA|x|) / (1 + lnA)
The companded data is also inverted as recommended by the G.711 standard (all 8 bits are inverted
for µ-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 (µ-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).
8-bit mode is selected whenever DAC_COMP=1 or ADC_COMP=1. The use of 8-bit data allows
samples to be passed using as few as 8 BCLK cycles per LRC frame. When using DSP mode B, 8-
bit data words may be transferred consecutively every 8 BCLK cycles.
8-bit mode (without Companding) may be enabled by setting DAC_COMPMODE=1 or
ADC_COMPMODE=1, when DAC_COMP=0 and ADC_COMP=0.
Table 75 8-bit Companded Word Composition
SIGN
R6 (06h)
REGISTER
BIT7
ADDRESS
BIT
4
3
2
1
EXPONENT
DAC_COMP
DAC_COMPMODE
ADC_COMP
ADC_COMPMODE
BIT[6:4]
LABEL
-1 ≤ x ≤ 1
} for x ≤ 1/A
} for 1/A ≤ x ≤ 1
DEFAULT
0b
0b
0b
0b
DAC Companding Enable
0 = disabled
1 = enabled
DAC Companding Type
0 = µ-law
1 = A-law
ADC Companding Enable
0 = disabled
1 = enabled
ADC Companding Type
0 = µ-law
1 = A-law
MANTISSA
BIT[3:0]
DESCRIPTION
PP, April 2009, Rev 3.0
WM8400
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