WM8974GEFL/V Wolfson Microelectronics, WM8974GEFL/V Datasheet - Page 53

• Manufacturer Part Number: WM8974GEFL/V
• Description: Audio CODECs Mono Codec with Spkr
• Manufacturer: Wolfson Microelectronics

Specifications of WM8974GEFL/V

• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: QFN-24
• Minimum Operating Temperature: - 25 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Production Data
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Table 49 Companding Control
Table 50 8-bit Companded Word Composition
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 MSB’s
of data.
Companding converts 13 bits (µ-law) or 12 bits (A-law) to 8 bits using non-linear quantization. The
input data range is separated into 8 levels, allowing low amplitude signals better precision than that
of high amplitude signals. This is to exploit the operation of the human auditory system, where
louder sounds do not require as much resolution as quieter sounds. The companded signal is an 8-
bit word containing sign (1-bit), exponent (3-bits) and mantissa (4-bits).
SIGN
R5
Companding
control
REGISTER
BIT7
ADDRESS
EXPONENT
0
2:1
4:3
BIT
LOOPBACK
ADC_COMP
DAC_COMP
BIT[6:4]
LABEL
-1 ≤ x ≤ 1
} for x ≤ 1/A
} for 1/A ≤ x ≤ 1
0
0
0
DEFAULT
MANTISSA
Digital loopback function
0=No loopback
1=Loopback enabled, ADC data output is fed
directly into DAC data input.
ADC companding
00=off
01=reserved
10=µ-law
11=A-law
DAC companding
00=off
01=reserved
10=µ-law
11=A-law
BIT[3:0]
PD, Rev 4.5, September 2008
DESCRIPTION
WM8974
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