Cirrus Logic CS53L21 - Manual (Page 27)

DS700PP1 27
CS53L21
4.3.8 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.
Maximum noise gate attenuation levels will depend on the gain applied in either the PGA or MIC pre-am-
plifier. For example: If both +32 dB pre-amplification and +12 dB programmable gain is applied, the max-
imum attenuation that the noise gate achieves will be 52 dB (-96 + 32 + 12) below full-scale.
Ramp-down time to the maximum setting is affected by the SOFTx bit.
Recommended settings: For best results, enable soft ramp for the digital attenuator. When the analog in-
puts are configured for differential signals (see
“Differential Inputs” on page 23“Differential Inputs” on
page 23 ), enable the NG_ALL bit to trigger the noise gate only when both inputs fall below the threshold.
Software
Controls: “Noise Gate Configuration & Misc. (Address 1Fh)” on page 54 , “ADC Control (Address 06h)” on
page 45 .
-96 -40
THRESH[2:0]
Max
imum A
tte
n
ua
tio
n
*
-52 dB
Output
(dB)
Input (dB)
NG
EN
=1
NG
EN
=0
-80 dB
-64 dB
Figure 11. Noise Gate Attenuation