Cirrus Logic CS42L52 - Manual (Page 27)

DS680F2 27
CS42L52
3/1/13
4.2.3 Noise Gate
The noise gate may be used to mute signal levels that fall below a programmable threshold. This prevents
the ALC from applying gain to noise. A programmable delay may be used to set the minimum time before
the noise gate attacks the signal.
Note: Maximum noise gate attenuation levels will depend on the gain applied in either the PGA or MIC
pre-amplifier. For example: If both +32 dB pre-amplification and +12 dB programmable gain is applied,
the maximum attenuation that the noise gate achieves will be 52 dB (-96 + 32 + 12) below full-scale.
Referenced Control Register Location
PGAxVOL[5:0
MAX[2:0], MIN[2:0] “PGAx Vol. and ALCx Transition Ctl.: ALC, PGA A (Address 12h) and ALC, PGA B (Address 13h)” on
page 55
“ALC Threshold (Address 2Ch)” on page 68
Referenced Control Register Location
Noise Gate Controls............ “Noise Gate Control (Address 2Dh)” on page 69
O u tp u t
(a fte r A L C )
In p u t (b e fo re A L C )
R R A T E [5 :0 ]
P G A G a in a n d /o r
A tte n u a to r
A L C
R e s p o n s e
M A X [2 :0 ]
A R A T E [5 :0
]
b e lo w fu ll s c a le
M IN [2 :0 ]
b e lo w fu ll s c a le
M IN [2 :0 ]
b e lo w fu ll s c a le
M A X [2 :0 ]
b e lo w fu ll s c a le
Figure 8. ALC
-96 -40
THRESH[2:0]
Ma
xi
mu
m At
te
nu
a ti
o n*
-52 dB
Output
(dB)
Input (dB)
N
G
E
N
=1
N
G
E N
=0
-80 dB
-64 dB
Figure 9. Noise Gate Attenuation