WM8985GEFL Wolfson Microelectronics, WM8985GEFL Datasheet - Page 84

• Manufacturer Part Number: WM8985GEFL
• Description: Audio CODECs Multimedia CODEC with Class D HP
• Manufacturer: Wolfson Microelectronics

Specifications of WM8985GEFL

• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: QFN-32
• Minimum Operating Temperature: - 25 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

WM8985
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Table 50 8-bit Companded Word Composition
Figure 39 μ-Law Companding
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).
Setting the WL8 register bit allows the device to operate with 8-bit data. In this mode it is possible to
use 8 BCLK’s per LRC frame. When using DSP mode B, this allows 8-bit data words to be output
consecutively every 8 BCLK’s and can be used with 8-bit data words using the A-law and u-law
companding functions.
SIGN
BIT7
120
100
80
60
40
20
0
0
0.1
EXPONENT
BIT[6:4]
0.2
0.3
-1 ≤ x ≤ 1
u-law Companding
0.4
Normalised Input
} for x ≤ 1/A
} for 1/A ≤ x ≤ 1
0.5
0.6
0.7
MANTISSA
BIT[3:0]
0.8
0.9
PD, Rev 4.6, July 2009
1
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Production Data
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