CS4299-BQ Datasheet, PDF (37/52 Pages) Cirrus Logic – CrystalClear SoundFusion Audio Codec 97

CS4299-BQ
6.1.3 Microphone Inputs
Figure 13 illustrates an input circuit suitable for dy-
namic and electret microphones. Electret, or phan-
tom-powered, microphones use the right channel
(ring) of the jack for power. The design also sup-
ports the recommended advanced frequency re-
sponse for voice recognition as specified in PC 99.
Note the microphone input to the CS4299-BQ has
an integrated pre-amplifier. Using the 20dB bit in
the Microphone Volume Register (Index 0Eh) the
pre-amplifier gain can be set to 0 dB or 20 dB.
Figure 14 shows an external pre-amplifier circuit
for an additional 18 dB gain.
2 kΩ
47 kΩ
0.33 µF _{47 Ω}
100 pF
NPO
6.8 K Ω
+
1 µF
MC33078 or
MC33178
47 kΩ
+ 0.1 µF
0.33 µF
X7 R
Vrefout
MIC1
or
MIC2
220 pF
NPO
3.3 µF
Figure 13. Microphone Input
6.1.4 PC Beep Input
The PC_BEEP input is useful for mixing the output
of the “beeper” (timer chip), provided in most PCs,
with the other audio signals. When the CS4299-BQ
is held in reset, PC_BEEP is passed directly to the
line output. This allows the system sounds or
“beeps” to be available before the AC ’97 interface
has been activated. Figure 15 illustrates a typical
input circuit for the PC_BEEP input. If PC_BEEP
is driven from a CMOS gate, the 4.7 kΩ resistor
should be tied to analog ground instead of +5VA.
Although this input is described for a low-quality
“beeper”, it is of the same high-quality as all other
analog inputs and may be used for other purposes.
+5VA (Low Noise) or
AGND if CMOS Source
PC-BEEP-BUS
4.7 kΩ
47 kΩ
2.7 nF
X7R
AGND
0.1 µ F
X7R
PC_BEEP
Figure 15. PC_BEEP Input
+5 VA
68 kΩ
+5 VA
U1A
1
8
+ ^{3 MC33078D}
-2
4
AGND
47 kΩ
+
10 µF
47 kΩ
100 kΩ
2.7 kΩ
47 kΩ
4
AGND
3
5
2
0.068 µF
1
X7R
220 pF 220 pF
AGND
6.8 kΩ
+ _{10 µF}
CGND
AGND
AGND
AGND
+5 VA _U1B
5+
8
MC33078D
7
6-
1 µF
MIC1/MIC2
4
X7R
AGND
220 pF
47 kΩ
Figure 14. Microphone Pre-amplifier
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