CS4298 Datasheet, PDF (38/52 Pages) Cirrus Logic – SoundFusion Audio/Modem Codec 97 (AMC 97)

CS4298
7.2 Microphone Level Inputs
The microphone level inputs, MIC1 and MIC2, include a selectable -34.5 dB to +12 dB gain stage
for interfacing to an external microphone. An additional 20 dB gain block is also available. Figure 12
illustrates a single-ended microphone input buffer circuit that will support lower gain mics. The cir-
cuit in Figure 12 supports dynamic mics and phantom-powered mics that use the right channel (ring)
of the jack for power..
7.3 Line Level Outputs
The analog output section provides a stereo line-level output and an alternate stereo line-level output.
LINE_OUT_L, LINE_OUT_R, ALT_LINE_OUT_L, and ALT_LINE_OUT_R outputs should be
capacitively coupled to external circuitry.
The mono output, MONO_OUT, can be used as either a sum of the left and right output channels
attenuated by 6 dB to prevent clipping at full scale or the selected MIC_IN signal. The mono out
channel can be used to drive the PC internal mono speaker using an appropriate drive circuit. This
approach allows the traditional PC sounds to be integrated with the rest of the audio system. The mute
control is independent of the line outputs allowing the mono channel to mute the speaker without
muting the line outputs.
Each of the 5 analog outputs, if used in the design, require 680 pF or larger NPO dielectric capacitors
between the corresponding pin and AGND. Each analog output is DC biased up to the Vrefout volt-
age signal reference which is nominally 2.2 V. This requires that the output either be AC coupled to
external circuitry (AC load must be greater than 10 kΩ) or DC coupled to a buffer op-amp biased at
the Vrefout voltage (see Figure 13 for the recommended headphone op-amp circuit).
68 kΩ
+5 VA
U1A
1
8
+ ^{3 MC33078D}
-2
4
AGND
+5 VA
47 kΩ
+¹
10 µF
2
47 kΩ
100 kΩ
AGND
AGND
2.7 kΩ
47 kΩ
4
AGND
3
5
2
0.068 µF
1
X7R
220 pF 220 pF
AGND
CGND
+1
6.8 kΩ
10 µF
2
AGND
+5 VA _U1B
5₊
8
MC33078D
7
1 µF
6-
4
X7R ^MIC1
AGND
220 pF
47 kΩ
Figure 12. PC ‘99 Microphone Pre-amplifier
38
DS315PP2