FAB2200 Datasheet, PDF (20/33 Pages) Fairchild Semiconductor – Audio Subsystem with Stereo Class-G Headphone Amplifier and 1.2W Mono Class-D Speaker Amplifier

Programmable Speaker Amplifier Noise Gate
The speaker noise gate automatically mutes the speaker
amplifier when its input amplitude is low to reduce noise
during inactivity. This function is not recommended for
music playback, but is effective for speech. The amplitude
is measured after input pre-amplifiers, but before the
speaker amplifier’s volume control. The speaker noise
gate’s threshold level is set by the SPNGTHRESH
register. The amplitude must be less than the speaker
noise gate threshold for a time determined by the
SPNGTIME register. When the speaker noise gate mutes
the speaker amplifier, the SPNGTRIP bit is set to 1.
If the input amplitude goes above the speaker noise
gate threshold, the speaker amplifier is un-muted and
the SPNGTRIP bit is set to 0. If the AGC is not enabled,
the speaker amplifier is returned to its former
PRESENTGAIN value. If the AGC is enabled,
AGCRELEASE speed determines the new
PRESENTGAIN value.
Table 14. Speaker Noise Gate Threshold Voltage
SPNGTHRESH [2:0]
000
001
010
011
100
101
110
111
Table 15.
Speaker Noise Gate Timing
SPNGTIME [2:0]
000
001
010
011
100
101
110
111
Speaker Noise Gate Threshold (mVpk)
Speaker Noise Gate Disabled
2.8
5.7
11.3
22.6
45.3
90.5
181.0
Time (ms)
10
20
40
80
160
320
640
Reserved
© 2009 Fairchild Semiconductor Corporation
FAB2200 • Rev. 1.0.1
20
www.fairchildsemi.com