CS4231A Datasheet, PDF (13/76 Pages) List of Unclassifed Manufacturers – PARALLEL INTERFACE MULTIMEDIA AUDIO CODEC

CS4231A
Line-Level Inputs plus MPC Mixer
The analog input interface is designed to accom-
modate four stereo inputs and one mono input.
Three of these sources are multiplexed to the
ADC. These inputs are: a stereo line-level input
(LINE), a stereo microphone input (MIC), and a
stereo auxiliary line-level input (AUX1). The
LINE and AUX1 inputs have a separate path,
with volume control, to the output analog mixer
which has the additional inputs of a stereo
AUX2 channel, a mono input channel, and the
output of the DACs. All audio inputs should be
capacitively coupled to the CS4231A.
Since some analog inputs can be as large as
2 V_RMS, the circuit shown in Figure 2 can be
used to attenuate the analog input to 1 V_RMS
which is the maximum voltage allowed for the
line-level inputs on the CS4231A.
5.6 kΩ
5.6 kΩ
0.33 µF
R
0.33 µF
L
5.6 kΩ 5.6 kΩ
Figure 2. Line Inputs
Microphone Level Inputs
The microphone level inputs, LMIC and RMIC,
include a selectable + 20dB gain stage for inter-
facing to an external microphone. The 20 dB
gain block can be turned off to provide another
stereo line-level input. Figure 3 illustrates a sin-
gle-ended microphone input buffer with +18 dB
of gain that will support lower gain mics, and
should be placed as close to the input jack as
possible to minimize noise coupling.
Mono Input with Attenuation and Mute
The mono input, MIN, is useful for mixing the
output of the "beeper" (timer chip), provided in
DS139PP2
1.5 kΩ
+
10 µF
+
1 µF
11 kΩ
560 pF
NPO
0.33 µF
29 _LMIC
MC33078 or
MC33178
32 _VREF
47 kΩ
+
10 µF
Figure 3. Left or Mono Microphone Input
all PCs, with the rest of the audio signals. The
attenuation control allows 16 levels in -3dB
steps. In addition, a mute control is provided.
The attenuator is a single channel block with the
resulting signal sent to the output mixer where it
is mixed with the left and right outputs. Figure 4
illustrates a typical input circuit for the Mono In.
Although this input is described for a low-qual-
ity beeper, the input is of the same high-quality
as all other analog inputs and may be used for
other purposes. At power-up, the MIN line is un-
muted (as is the mono out line) allowing the
initial beeps heard, when the computer is initial-
izing, to pass through.
+5VA
(Low Noise)
4.7 kΩ
1 47 kΩ
46 _MIN
0.1 µF
2.7 nF
Figure 4. Mono Input
Analog Outputs
The analog output section of the CS4231A pro-
vides a stereo line-level output. The other output
types (headphone and speaker) can be imple-
mented with external circuitry. LOUT and
ROUT outputs should be capacitively coupled to
external circuitry.
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