CS4228A Datasheet, PDF (13/32 Pages) Cirrus Logic – 24-Bit, 96 kHz Surround Sound Codec

CS4228A
The high pass filters can be disabled by setting the
HPF bit in the ADC Control register. When assert-
ed, any DC present at the analog inputs will be rep-
resented in the ADC outputs. The high pass filter
may also be “frozen” using the HPFZ bit in the
ADC Control register. In this condition, it will re-
member the DC offset present at the ADC inputs at
the moment the HPFZ bit was asserted, and will
continue to remove this DC level from the ADC
outputs. This is useful in cases where it is desirable
to eliminate a fixed DC offset while still maintain-
ing full frequency response down to DC.
3.3 Analog Outputs
3.3.1 Line Level Outputs
The CS4228A contains on-chip buffer amplifiers
capable of producing line level outputs. These am-
plifiers are biased to a quiescent DC level of ap-
proximately 2.3 V. This bias, as well as variations
in offset voltage, are removed using off-chip AC
load coupling.
The delta-sigma conversion process produces high
frequency noise beyond the audio passband, most
of which is removed by the on-chip analog filters.
The remaining out-of-band noise can be attenuated
using an off-chip low pass filter. For most applica-
tions, a simple passive filter as show in Figure 7 can
be used. Note that this circuit also serves to block
the DC present at the outputs. Figure 8 gives an ex-
ample of a filter which can be used in applications
where greater out of band attenuation is desired.
The 2-pole Butterworth filter has a -3 dB frequency
of 50 kHz, a passband attenuation of 0.1 dB at
20 kHz providing optimal out-of-band filtering for
sample rates from 44.1 kHz to 96 kHz. The filter
has and a gain of 1.56 providing a 2 Vrms output
signal.
3.3.2 Digital Volume Control
Each DAC’s output level is controlled via the Dig-
ital Volume Control register operating over the
range of 0 to 90.5 dB attenuation with 0.5 dB reso-
lution. Volume control changes do not occur in-
stantaneously. Instead they ramp in increments of
0.125 dB at a variable rate controlled by the
RMP1:0 bits in the Digital Volume Control regis-
ter.
MUTEC
10 k
10 k
AOUT
22 µF
560
+
100 k
C=142µF
F_s
2SC2878
or
2SC3326
MUN2IIIT1
MUTEDRV
Line Out
C
2.2 k
Figure 7. Passive Output Filter with Mute
1 nf
AOUT
3.57 k
3.57 k
5_
1 nf ⁶ ₊
7
MC33078
GND
+
10 µf
3.57 k
2k
+
10 µf
MUTE
MUTE DRV
Line
Out
2 VRMS
100 pf
2-Pole Butterworth Filter
Figure 8. Butterworth Output Filter with Mute
DS511PP1
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