CS4298 datasheet(37/52 Pages) CIRRUS

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CS4298

DS315PP2

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 VRMS, the circuit shown in Figure 10 can be used to

attenuate the analog input by 6 dB (to 1 VRMS) 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 k

Ω

6.8 k

Ω

1.0

µF

1.0

µF

6.8 k

Ω

6.8 k

Ω

Figure 10. Line Inputs

Figure 11. Differential CDROM In

6.8 k

Ω

6.8 k

Ω

1.0

µF

1.0

µF

CD_L

CD_R

6.8 k

Ω

6.8 k

Ω

3.4 k

Ω

CD_GND

2.0

µF

3.4 k

Ω

(All resistors 1%)

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