SAA8200HL Datasheet, PDF (39/71 Pages) NXP Semiconductors – Ensation Base integrated wireless audio baseband

Philips Semiconductors
SAA8200HL
Ensation Base integrated wireless audio baseband
7.19.2.5 Mute
When the left and right channel of the decimator are muted (bit EN_MUTE is a logic 1),
the gain in the decimator is decreased linearly to −63.5 dB with a final step to mute at a
rate of 0.5 dB per f_s period (dB linear). This is done to avoid harsh audible plops. The time
required for a complete mute depends on the initial gain setting. Maximum required time is
256 f_s periods. When a complete mute is achieved for both left and right channels, the bit
MUTE_STATE (SADC_CTRL_DECO[0]) is made logic 1. When the channels are
de-muted (bit EN_MUTE is a logic 0) the gain of the decimator is increased at the same
rate until the programmed gain setting is achieved.
7.19.2.6 Overflow detection
The output signal is used to indicate whenever the output data, in either the left or right
channel, is larger than −1.16 dB of the maximum possible digital swing. When this
condition is detected the overflow bit (SADC_CTRL_DECO[1]) is forced to a logic 1 for at
least 512 f_s cycles (11.6 ms at f_s = 44.1 kHz) allowing even a slow microcontroller to poll
this event. This time-out is reset for each infringement.
7.19.2.7 AGC function
The decimation filter is equipped with an Automatic Gain Control (AGC) block. This
function is intended, when enabled, to keep the output signal at a constant level.
The AGC can be used for microphone applications in which the distance to the
microphone is not always the same.
The AGC can be enabled via the control register (SADC_CTRL_DECI[23]). In this case it
bypasses the digital volume control. Other features of the AGC, such as the attack, decay
and target level can be set via the same register.
The DC filter in front of the decimation filter must be enabled when AGC is in operation,
otherwise the output will be disturbed by the DC offset added in the ADC.
Table 19: AGC enable control
AGC_EN
AGC function
0
disabled, manual gain control via the left/right decimator volume
control, (default)
1
enabled, with manual microphone gain settings via PGA
Table 20: AGC target level settings
AGC_LEVEL1
AGC_LEVEL0
0
0
0
1
1
0
1
1
AGC target level value (dB)
−5.5
−8.0
−11.5
−14.0
SAA8200HL_2
Preliminary data sheet
Rev. 02 — 17 October 2005
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
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