CS4299 datasheet(36/52 Pages) CIRRUS

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CS4299

6. ANALOG HARDWARE

DESCRIPTION

The analog line-level input hardware consists of

four stereo inputs (LINE_IN_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 line-level output hardware consists of a mono

output (MONO_OUT), and dual stereo line outputs

(LINE_OUT_L/R and ALT_LINE_OUT_L/R).

This section describes the analog hardware needed

to interface with these pins. The designs presented

in this section comply with specifications detailed

in Chapter 17 of the Microsoft PC Design Guide-

lines [7] (referred to as PC 99). For EMI reduction

techniques refer to the application note N165:

CS4297A/CS4299 EMI Reduction Techniques [5].

6.1

Analog Inputs

All analog inputs to the CS4299, 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 VRMS. For the microphone

input the maximum allowed voltage depends on the

selected boost setting.

6.1.1

Line-Level Inputs

Figure 10 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 VRMS, to the CS4299 maximum allowed 1 VRMS.

6.1.2

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 11 and

Figure 12 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 11 can be used to attenuate

a 2 VRMS CD input signal by 6 dB. The circuit

shown in Figure 12 can be used for a 1 VRMS CD in-

put signal.

6.8 k

Ω

6.8 k

Ω

1.0

µF

1.0

µF

6.8 k

Ω

6.8 k

Ω

Figure 10. Line Input (Replicate for Video and Aux)

(All resistors 1%)

6.8 k

Ω

CD_L

CD_COM

CD_R

1.0

µF

CD_L

CD_R

CD_GND

6.8 k

Ω

1.0

µF

3.4 k

Ω

6.8 k

Ω

2.2

µF

3.4 k

Ω

6.8 k

Ω

AGND

Figure 11. Differential 2 V

RMS CD Input

100

Ω

CD_L

CD_COM

CD_R

1.0

µF

CD_L

CD_R

CD_GND

100

Ω

1.0

µF

100

Ω

47 k

Ω

2.2

µF

47 k

Ω

47 k

Ω

AGND

Figure 12. Differential 1 V

RMS CD Input

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