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AS3421 AS3422

Datasheet - D e t a i l e d D e s c r i p t i o n

9.3 Headphone Output

The headphone output is a true ground output using VNEG as negative supply, designed to provide the audio signal with 2x12mW @ 16

Ω-64Ω,

which are typical values for headphones. It is also capable to operate in bridged mode for higher impedance (e.g. 300

Ω) headphone. In this

mode the left output is carrying the inverted signal of the right output shown in Figure 20.

Figure 19. Headphone Output Single Ended Mode

Figure 20. Headphone Output Differential Mode

9.3.1

Input Multiplexer

The signal from the line-input gain stage gets summed at the input of the headphone stage with the microphone gain stage output, the first filter

opamp output or the second filter opamp output. The microphone gain stage output is used per default. It is also possible to playback without

ANC by only using the line-input gain stage with no other signal on the multiplexer.

For the monitor mode, the setting of this input multiplexer can be changed to another source, normally to the microphone.

9.3.2

No-Pop Function

The No-Pop startup of the headphone stage takes 60ms to 120ms dependent on the supply voltage.

9.3.3

No-Clip Function

The headphone output stage gets monitored by comparator stages which detect if the output signal starts to clip.

This signal is used to reduce the LineIn gain to avoid distortion of the output signal. A hystereses avoids jumping between 2 gain steps for a

signal with constant amplitude.

Pop

Click

Control

HPR

HPL

AGND

LineInR

QOP2R

QOP1R

QMicR

LineInL

QOP2L

QOP1L

QMicL

HPVSS

HPVDD

open

LineIn

gain stage

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