AK7755EN_16 Datasheet, PDF (87/109 Pages) Asahi Kasei Microsystems – DSP with Mono ADC Stereo CODEC + Mic/Lineout Amp

[AK7755]
■ ADC Block
1. ADC High Pass Filter
A digital High Pass Filter (HPF) is integrated for DC offset cancellation of the ADC input. The cut-off
frequency of the HPF is approximately 1Hz (at fs=48kHz).
fs
Cut-off frequency
48kHz
3.73Hz
44.1kHz
3.43Hz
8kHz
0.62Hz
2. ADC Soft Mute
2-1. Description
The ADC block has a digital soft mute circuit. The soft mute operation is performed in the digital
domain. The output signal is attenuated to -∞ in “ADC Digital Volume Level x ATT transition time”
from the current ADC Digital Volume Setting Level by setting ADMUTE and AD2MUTE bits to “1”.
When the ADMUTE (CONT1A: D7) and AD2MUTE (CONT1A: D6) bits are returned to “0”, the
mute is cancelled and the output attenuation gradually changes to ADC Digital Volume Setting Level
in “ADC Digital Volume Level x ATT transition time”. If the soft mute is cancelled before attenuating
to -∞ after starting the operation, the attenuation is discontinued and returned to ADC Digital Volume
Setting Level by the same cycle. The soft mute is effective for changing the signal source without
stopping the signal transmission. The transition time from 0dB to -∞ and vice versa is 828 LRCK
cycles.
The soft mute function works when the ADC is in operation. The attenuation value is initialized by the
PDN pin = “L”.
SMUTE Register Value
0dB
Attenuation
-∞dB
Output Image
Group Delay (GD)
Group Delay (GD)
828/fs
828/fs
Figure 71. ADC Soft Mute
2-2. Input Selector Switching Sequence
The input selector should be changed after soft muting to avoid the switching noise of the input
selector.
· Input Selector Switching Sequence
1. Enable soft mute before changing the channel.
2. Change the Channel.
3. Disable softer mute.
ADMUTE
(2)
DATT Level
(1)
(1)
Attenuation
(3)
-∞
Channel
IN1/IN3
IN2/IN4
Figure 72. ADC Input Channel Switching Sequence Example
014006643-E-00
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2014/10