cs4237b Cirrus Logic, Inc., cs4237b Datasheet - Page 91

• Manufacturer Part Number: cs4237b
• Description: Crystalclear Advanced Audio System With 3d Sound
• Manufacturer: Cirrus Logic, Inc.

The AUX2 line-level inputs have an extra pin,
CMAUX2, which provides a pseudo-differential
input for both LAUX2 and RAUX2. This pin
takes the common-mode noise out of the AUX2
inputs when connected to the ground coming
from the AUX2 analog source. Connecting the
AUX2 pins as shown in Figure 27 provides extra
noise attenuation coming from the CDROM
drive, thereby producing a higher quality signal.
Since the better the resistors match, the better the
common-mode attenuation, one percent resistors
are recommended. If CMAUX2 is not used, it
should be connected through an AC cap to ana-
log ground.
Microphone Level Inputs
The microphone level inputs, LMIC and RMIC,
include a selectable -22.5 dB to +22.5 dB gain
stage for interfacing to an external microphone.
An additional 20 dB gain block is available in
the path to the output mixer. The 20 dB gain
block can be switched off to provide another ste-
reo line-level input. Figure 28 illustrates a
single-ended microphone input buffer circuit that
will support lower gain mics. If a mono micro-
phone is all that is desired, the RMIC input
should be connected to the output of the mono
op amp, used for LMIC, through its own AC
coupling capacitor. The circuit in Figure 28 sup-
ports dynamic mics and phantom-powered mics
that use the right channel of the jack for power.
DS213PP4
6.8 k
6.8 k
Figure 27. Differential CDROM In
6.8 k
(All resistors 1%)
3.4 k
3.4 k
1.0 F
1.0 F
6.8 k
1.0 F
CMAUX2
RAUX2
LAUX2
Mono Input
The mono input, MIN, is useful for mixing the
output of the "beeper" (timer chip), provided in
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. Fig-
ure 29 illustrates a typical input circuit for the
Mono In. If MIN is driven from a CMOS gate,
the 4.7k
VA+. Although this input is described for a low-
quality 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 connected directly to the MOUT pin
(with 9 dB of attenuation) allowing the initial
beeps, heard when the computer is initializing, to
pass through.
Figure 28. Left or Mono Microphone Input
1
2 k
600
AGND - if CMOS Source
47 k
0.1 F
should be tied to AGND instead of
+5VA (Low Noise) or
2.7 nF
47 k
Figure 29. Mono Input
+
MC33078 or
MC33178
10 F
4.7 k
2.7 nF
NPO
4.7 k
0.1 F
+
X7R
0.33 F
1 F
0.33 F
47 k
MIN
CS4237B
VREF
LMIC
RMIC
91