CS4298 Datasheet, PDF (37/52 Pages) Cirrus Logic – SoundFusion Audio/Modem Codec 97 (AMC 97)

CS4298
7. ANALOG HARDWARE DESCRIPTION
The analog hardware consist of a four line-level stereo inputs, two selectable mono microphone in-
puts, two mono inputs, a mono output, and dual, independent stereo line outputs. This section de-
scribes the analog hardware needed to interface with these pins.
7.1 Line-Level Inputs
The analog inputs consist of four stereo analog inputs and four mono inputs. As shown in Figure 8,
the input to the ADCs comes from the Input Mux which selects one of the following: Phone (Mono),
Aux, Video, CD, Mic1 or Mic2 (Mono), Line, Stereo Output Mix, or the Mono Output Mix (Mono).
Unused analog inputs should be connected together and then connected through a capacitor to analog
ground or tied to the Vrefout line directly.
The analog input mixer is designed to accommodate five stereo inputs and one mono input. These
inputs are: a stereo line-level input (LINE), a mono microphone input (MIC), a stereo CD-ROM in-
put (CD), a stereo auxiliary line-level input (AUX), and the PCM output from the DACs. Each of the
stereo inputs has separate volume controls for each channel and one mute control for each left/right
pair. The mono microphone input has one mute and one volume control.
The inputs to the output mixer are: the input mixer output, the PC Beep mono input, and the Phone
mono input.
All analog inputs to the CS4298, including CD_GND, should be capacitively coupled to the input
pins.
Since many analog levels can be as large as 2 V_RMS, the circuit shown in Figure 10 can be used to
attenuate the analog input by 6 dB (to 1 V_RMS) which is the maximum voltage allowed for all the
stereo line-level inputs: LINE_IN, AUX_IN, and VIDEO_IN.
The CD line-level inputs have an extra pin, CD_GND, which provides a pseudo-differential input for
both CD_L and CD_R. This pin takes the common-mode noise out of the CD inputs when connected
to the ground coming from the CD analog source. Connecting the CD pins as shown in Figure 11
provides extra attenuation of common mode noise coming from the CDROM drive, thereby produc-
ing a higher quality signal. One percent resistors are recommended since the better the resistors
match, the better the common-mode attenuation of unwanted signals. If CD is not used, the inputs
should be connected through AC capacitors to analog ground or connected to Vrefout.
6.8 kΩ
6.8 kΩ
6.8 kΩ
1.0 µF
R
1.0 µF
L
6.8 kΩ
Figure 10. Line Inputs
DS315PP2
(All resistors 1%)
6.8 kΩ
3.4 kΩ
1.0 µF
2.0 µF
CD_L
CD_GND
CD_R
6.8 kΩ
6.8 kΩ
1.0 µF
3.4 kΩ ^{6.8 kΩ}
Figure 11. Differential CDROM In
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