WM8776SEFT/V Wolfson Microelectronics, WM8776SEFT/V Datasheet - Page 38

• Manufacturer Part Number: WM8776SEFT/V
• Description: Audio CODECs Stereo CODEC with 5-Ch Mux
• Manufacturer: Wolfson Microelectronics

Specifications of WM8776SEFT/V

• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: TQFP-48
• Minimum Operating Temperature: - 25 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

WM8776
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NOISE GATE (ALC ONLY)
When the signal is very quiet and consists mainly of noise, the ALC function may cause “noise
pumping”, i.e. loud hissing noise during silence periods. The WM8776 has a noise gate function that
prevents noise pumping by comparing the signal level at the AINL1/2/3/4/5 and/or AINR1/2/3/4/5 pins
against a noise gate threshold, NGTH. The noise gate cuts in when:
•
This is equivalent to:
•
When the noise gate is triggered, the PGA gain is held constant (preventing it from ramping up as it
would normally when the signal is quiet).
The table below summarises the noise gate control register. The NGTH control bits set the noise
gate threshold with respect to the ADC full-scale range. The threshold is adjusted in 6dB steps.
Levels at the extremes of the range may cause inappropriate operation, so care should be taken with
set–up of the function. Note that the noise gate only works in conjunction with the ALC function, and
always operates on the same channel(s) as the ALC (left, right, both, or none).
REGISTER
Noise Gate
ADDRESS
R19 (13h)
0010011
Signal level at ADC [dB] < NGTH [dB] + PGA gain [dB] + Mic Boost gain [dB]
Signal level at input pin [dB] < NGTH [dB]
Control
4:2
BIT
0
NGTH[2:0]
LABEL
NGAT
DEFAULT
000
0
1 = enable
0 = disable
Noise gate threshold (with respect to
ADC output level)
000: -78dBFS
001: -72dBfs
… 6 dB steps
110: -42dBFS
111: -36dBFS
Noise gate function enable
PD, Rev 4.1, September 2008
DESCRIPTION
Production Data
38