WM8777
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RECOMMENDED ANALOGUE OUTPUT EXTERNAL COMPONENTS
It may be that a lowpass filter is required to be applied to the output from each DAC channel for Hi Fi
applications. Typically a second order filter is suitable and provides sufficient attenuation of high
frequency components (the unique low order, high bit count multi-bit sigma delta DAC structure used
in WM8777 produces much less high frequency output noise than competitors devices). This filter is
typically also used to provide the 2x gain needed to provide the standard 2Vrms output level from
most consumer equipment. Figure 45 shows a suitable post DAC filter circuit, with 2x gain.
Alternative inverting filter architectures might also be used with as good results.
1.0nF
10uF
1.8kΩ
7.5kΩ
51
VOUT1L
47kΩ
680pF
4.7kΩ
4.7kΩ
OP_FIL
VOUT1R
VOUT2L
VOUT2R
VOUT3L
VOUT3R
VOUT4L
VOUT4R
OP_FIL
OP_FIL
OP_FIL
OP_FIL
OP_FIL
OP_FIL
OP_FIL
Figure 45 Recommended Post DAC Filter Circuit
PP Rev 1.94 November 2004
100
w
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
