ADAU1373BCBZ-R7 datasheet(39/296 Pages) AD

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ADAU1373

Rev. 0 | Page 39 of 296

THEORY OF OPERATION

Mono Differential Mode

ANALOG INPUTS

In mono differential mode, the AINxL/AINxP pins are used as

positive inputs, and the AINxR/AINxN pins are used as negative

inputs for the differential amplifier.

The ADAU1373 provides four stereo (unbalanced)/mono

differential inputs. Each input gain and mode of operation can

be set independently, using the I2C registers. Figure 82 shows the

typical input block for the stereo and mono differential inputs in

the programmable gain amplifier (PGA) modes and boost modes.

The input amplifers use AVDD as the supply voltage. The

AINxP/AINxN input pins are internally biased to AVDD/2,

which is the common-mode voltage for the amplifiers. The

common-mode pin (CM, Ball B9) must be decoupled using the

10 μF electrolytic capacitor, as well as a 100 nF, X7R ceramic

capacitor to keep the reference clean for lower noise. In addition,

the input pins must be provided with an ac coupling capacitor to

the desired source.

Each input can receive either a microphone or a line level signal.

Each input can be set to either stereo single-ended mode or mono

differential mode. In addition, the gain for the input amplifiers

can be set to PGA mode or boost mode. In PGA mode, the gain

can be varied from −12 dB to +18 dB (in 1 dB steps); whereas in

boost mode, it can be varied using one of the following three steps:

0 dB, 9 dB, or 20 dB. In PGA mode, the input resistance varies

as per the gain, with a minimum of ~5.6 kΩ. In boost mode,

the input resistance is constant at ~20 kΩ.

The typical value of the coupling capacitor can be calculated

using the desired 3 dB roll-off frequency, as follows:

Frequency f (3 dB) = 1/(2 × π × RIN × CIN)

(1)

Stereo Single-Ended Mode

where RIN = 5.6 kΩ.

In stereo single-ended mode, the AINxL/AINxP pins are used

as the left channel inputs, and the AINxR/AINxN pins are used

as the right channel inputs.

Typically, a 2.2 μF capacitor is recommended. This sets the

lower frequency cutoff, at 20 Hz, at approximately −1.5 dB.

VCM

STEREO PGA MODE

LEFT MIX

AINxL

AINxR

VCM

RIGHT MIX

VCM

STEREO BOOST MODE

LEFT MIX

AINxL

AINxR

VCM

RIGHT MIX

VCM

DIFFERENTIAL BOOST MODE

LEFT MIX

AINxP

AINxN

VCM

RIGHT MIX

VCM

DIFFERENTIAL PGA MODE

LEFT MIX

AINxP

AINxN

VCM

Figure 82. Typical Input Block for Stereo/Mono Differential Inputs in PGA Modes and Boost Modes

ADAU1373BCBZ-R7 Datasheet(PDF) 39 Page - Analog Devices

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