CS4294SLASHCS4298 datasheet(50/66 Pages) CIRRUS

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CS4202

DS549PP2

10. ANALOG HARDWARE

DESCRIPTION

The analog input section consists of four stereo

line-level

inputs

(LINE_L/R,

CD_L/C/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),

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 CS4202, including CD_C,

should be capacitively coupled to the input pins.

Unused analog inputs should be tied together and

connected through a capacitor to analog ground or

tied to the Vrefout pin directly. The maximum al-

lowed voltage for analog inputs, except the micro-

phone input, is 1 VRMS. The maximum allowed

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 Video and Aux in-

puts. This design attenuates the input by 6 dB,

bringing the signal from the PC 99 specified

2VRMS, to the CS4202 maximum allowed 1 VRMS.

10.1.2

CD Input

The CD line-level input has an extra pin, CD_C,

providing a pseudo-differential input for both

CD_L

and

CD_R.

This

takes

the

common-mode noise out of the CD inputs when

connected to the CD analog source ground. Follow-

ing the reference design in Figure 19 provides extra

attenuation of common mode noise coming from

the CD-ROM drive, thereby producing a higher

quality signal. One percent resistors are recom-

mended since closely matched resistor values pro-

vide better common-mode attenuation of unwanted

signals. The circuit shown in Figure 19 can be used

for a 1 VRMS CD input signal.

10.1.3

Microphone Inputs

Figure 20 illustrates an input circuit suitable for dy-

namic and electret microphones. Electret, also

known as phantom-powered, microphones use the

right channel (ring) of the jack for power. The de-

sign also supports the recommended advanced fre-

quency response for voice recognition as specified

in PC 99 and PC 2001. The microphone input of the

CS4202 has an integrated pre-amplifier. Using

combinations of the 10dB bit in the Misc. Crystal

Control Register (Index 60) and the 20dB bit in the

LINE_IN_R

LINE_IN_L

6.8 k

Ω

1.0

µ F

1.0

µ F

AGND

6.8 k

Ω

6.8 k

Ω

6.8 k

Ω

Figure 18. Line Input (Replicate for Video and AUX)

100

Ω

CD_L

CD_COM

CD_R

1.0

µF

CD_L

CD_R

CD_C

100

Ω

1.0

µF

100

Ω

47 k

Ω

2.2

µF

47 k

Ω

47 k

Ω

AGND

Figure 19. Differential 1 V

RMS CD Input

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