CS4215 datasheet(9/52 Pages) CIRRUS

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1 Vrms. The CMOUT reference level is used to

level shift the signal. This level shifting allows

the line inputs to be DC coupled into the

CS4215. Minimum ADC offset results when the

line inputs are DC coupled (see Analog Charac-

teristics Table).

Figure 3 shows an AC coupled input circuit for

signals centered around 0 Volts. The anti-alias-

ing RC filter presents a low impedance at high

frequencies and should be driven by a low im-

pedance source.

Microphone Level Inputs

Internal amplifiers with a programmable 20 dB

gain block are provided for the microphone level

inputs, MINR and MINL. Figure 4 shows a sin-

gle-ended input microphone pre-amplifier stage

with a gain of 23 dB. AC coupling is mandatory

for these inputs since any DC offset on the input

will be amplified by the codec.

The 20 dB gain block may be disabled using the

MLB bit in Control Time Slot 1.

When dis-

abled, the inputs become line level with full

scale inputs of 1 Vrms.

Adjustable Input Gain

The signals from the microphone or the line in-

puts are routed to a programmable gain circuit

which provides up to 22.5 dB of gain in 1.5 dB

steps. Level changes only take effect on zero

crossings to minimize audible artifacts, often re-

ferred to as "zipper noise". The requested level

change is forced if no zero crossing is found af-

ter 511 frames (10.6 ms at a 48 kHz frame rate).

A separate zero crossing detector exists for each

channel.

Analog Outputs

The analog outputs of the DACs are routed via

an attenuator to a pair of line outputs, a pair of

MINR

1 uF

VA+

0.1 uF

560 pF

10 uF

2.2 k

22.1 k

1 uF

50 k

MINL

1 uF

560 pF

2.2 k

22.1 k

150

10 uF

50 k

NPO

CMOUT

C47

R57

(Mono)

MC33078 or

C46

MC33178

A =20 dB

0.47 uF

C48

0.01 uF

NPO

150

R56

0.01 uF

NPO

Microphone

Input Left

(pin 17)

Microphone

Input Right

(pin 15)

0.47 uF

C45

Figure 4. Optional Microphone Input Buffer

CS4215

DS76F2

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