CS4294SLASHCS4298 datasheet(65/81 Pages) CIRRUS

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CS4205

DS489PP4

12.1.3

Microphone Inputs

Figure 28 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

CS4205 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

Mic Volume Register (Index 0Eh) the pre-amplifier

gain can be set to 0 dB, 10 dB, 20 dB, or 30 dB.

12.1.4

PC Beep Input

The PC_BEEP input is useful for mixing the output

of the “beeper” (timer chip), provided in most PCs,

with the other audio signals. When the CS4205 is

held in reset, PC_BEEP is passed directly to the

line output. This allows the system sounds or

“beeps” to be available before the AC ’97 interface

has been activated. Figure 29 illustrates a typical

input circuit for the PC_BEEP input. If PC_BEEP

is driven from a CMOS gate, the 4.7 k

Ω resistor

should be tied to analog ground instead of +5VA.

Although this input is described for a low-quality

“beeper”, it is of the same high-quality as all other

analog inputs and may be used for other purposes.

12.1.5

Phone Input

One application of the PHONE input is to interface

to the output of a modem analog front end (AFE)

device so that modem dialing signals and protocol

negotiations may be monitored through the audio

system. Figure 30 shows a design for a modem

connection where the output is fed from the

CS4205 MONO_OUT pin through a divider. The

divider ratio shown does not attenuate the signal,

providing an output voltage of 1 VRMS. If a lower

output voltage is desired, the resistors can be re-

placed with appropriate values, as long as the total

load on the output is kept greater than 10 k

Ω. The

PHONE input is divided by 6 dB to accommodate

a line-level source of 2 VRMS.

12.2

Analog Outputs

The analog output section provides a stereo and a

mono output. The MONO_OUT, LINE_OUT_L,

and LINE_OUT_R pins require 680 pF to 1000 pF

NPO dielectric capacitors between the correspond-

ing pin and analog ground. Each analog output is

DC-biased up to the Vrefout voltage signal refer-

0.1

µ F

X7R

100

Ω

0.1

µ F

X7R

MIC1/MIC2

µF

ELEC

AGND

+5VA

2.2 k

Ω

1.5 k

Ω

AGND

Figure 28. Microphone Input

4.7 k

Ω

PC_BEEP

+5VA (Low Noise) or

AGND if CMOS Source

PC-BEEP-BUS

47 k

Ω

2.7 nF

X7R

0.1

µF

X7R

AGND

Figure 29. PC_BEEP Input

PHONE

MONO_OUT

PHONE

MONO_OUT

6.8 k

Ω

1.0

µF

0 Ω

6.8 k

Ω

1.0

µF

47 k

Ω

AGND

1000 pF

Figure 30. Modem Connection

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