WM8955BL
Production Data
DIGITAL FILTER CHARACTERISTICS
Depending on the MCLK frequency and sample rate selected, 4 different types of digital filter can be
used in the DAC, called Type 0, 1, 2 and 3 (see “Master Clock and Audio Sample Rates”). The
performance of Types 0 and 1 is listed in the table below, the responses of all filters is shown in the
following pages.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
0.416fs
+/-0.03
UNIT
DAC Filter Type 0 (USB mode, 250fs operation)
Passband
+/- 0.03dB
-6dB
0
0.5fs
Passband Ripple
Stopband
dB
dB
0.584fs
-50
Stopband Attenuation
f > 0.584fs
DAC Filter Type 1 (USB mode, 272fs or Normal mode operation)
Passband
+/- 0.03dB
-6dB
0
0.4535fs
+/- 0.03
0.5fs
Passband Ripple
Stopband
dB
dB
0.5465fs
-50
Stopband Attenuation
f > 0.5465fs
Table 30 Digital Filter Characteristics
MODE
0 (250 USB)
GROUP DELAY
11/FS
1 (256/272)
16/FS
2 (250 USB, 96k mode)
3 (256/272, 88.2/96k mode)
4/FS
3/FS
Table 31 DAC Filters
TERMINOLOGY
Stop Band Attenuation (dB) – the degree to which the frequency spectrum is attenuated (outside audio band)
Pass-band Ripple – any variation of the frequency response in the pass-band region
DAC FILTER RESPONSES
0.02
0
0.01
-20
0
-0.01
-40
-0.02
-60
-0.03
-0.04
-80
-0.05
-100
0
0.5
1
1.5
2
2.5
3
-0.06
Frequency (Fs)
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
Frequency (Fs)
Figure 20 DAC Filter Frequency Response – Type 0
Figure 21 DAC Filter Ripple – Type 0
PD Rev 4.1 February 2007
38
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
