CS4201 Datasheet, PDF (50/68 Pages) Cirrus Logic – CrystalClear Audio Codec 97 with headphone Amplifier

CS4201
10. ANALOG HARDWARE
DESCRIPTION
The analog input section consists of four stereo
line-level inputs (LINE_L/R, CD_L/GND/R,
VIDEO_L/R, and AUX_L/R), two selectable
mono microphone inputs (MIC1 and MIC2), and
two mono inputs (PC_BEEP and PHONE). The an-
alog output section consists of a mono output
(MONO_OUT), a stereo headphone output
(HP_OUT_L/R), and a stereo line-level output
(LINE_OUT_L/R). This section describes the ana-
log hardware needed to interface with these pins.
The designs presented in this section are compliant
with Chapter 17 of Microsoft’s^ PC 99 System De-
sign Guide [7] (referred to as PC 99) and Chapter
11 of Microsoft’s^ PC 2001 System Design Guide
[8] (referred to as PC 2001). For information on
EMI reduction techniques refer to the application
note AN165: CS4297A/CS4299 EMI Reduction
Techniques [5].
10.1 Analog Inputs
All analog inputs to the CS4201, including
CD_GND, should be capacitively coupled to the
input pins. Unused analog inputs should be tied to-
gether and connected through a capacitor to analog
ground or tied to the Vrefout pin directly. The max-
imum allowed voltage for analog inputs, except the
microphone input, is 1 V_RMS. The maximum al-
lowed voltage for the microphone input depends on
the selected boost setting.
10.1.1 Line Inputs
Figure 18 shows circuitry for a line-level stereo in-
put. Replicate this circuit for the Line, Video and
Aux inputs. This design attenuates the input by
6 dB, bringing the signal from the PC 99 specified
2 V_RMS, to the CS4201 maximum allowed 1 V_RMS.
10.1.2 CD Input
The CD line-level input has an extra pin,
CD_GND, providing 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 CD analog source ground. Follow-
ing the reference designs in Figure 19 and
Figure 20 provides extra attenuation of common
mode noise coming from the CD-ROM drive,
thereby producing a higher quality signal. One per-
cent resistors are recommended since closely
matched resistor values provide better com-
mon-mode attenuation of unwanted signals. The
circuit shown in Figure 19 can be used to attenuate
a 2 V_RMS CD input signal by 6 dB. The circuit
shown in Figure 20 can be used for a 1 V_RMS CD in-
put signal.
6.8 kΩ
6.8 kΩ
AGND
1.0 µ F
LINE_IN_R
1.0 µ F
LINE_IN_L
6.8 kΩ 6.8 kΩ
AGND
Figure 18. Line Input (Replicate for Video and AUX)
CD_R
CD_L
CD_COM
6.8 kΩ
6.8 kΩ
3.4 kΩ
1.0 µ F
1.0 µ F
2.2 µF
6.8 kΩ 6.8 kΩ 3.4 kΩ
(All resistors 1%)
AGND
CD_R
CD_L
CD_GND
Figure 19. Differential 2 V_RMS CD Input
CD_R
CD_L
CD_COM
100 Ω
100 Ω
100 Ω
1.0 µF
1.0 µ F
2.2 µF
47 kΩ 47 kΩ 47 kΩ
CD_R
CD_L
CD_GND
AGND
Figure 20. Differential 1 V_RMS CD Input
50
DS483PP3