wm9081 Wolfson Microelectronics plc, wm9081 Datasheet - Page 37

• Manufacturer Part Number: wm9081
• Description: Mono Dac With 2.6w Class Ab/d Speaker Driver, Dynamic Range Controller And Retune Mobile Parametric Equalizer
• Manufacturer: Wolfson Microelectronics plc

Pre-Production
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Note that the Anti-Clip feature operates entirely in the digital domain, i.e. on the input path to the
DAC. It cannot be used to prevent signal clipping in the analogue domain (e.g. in the output PGA),
nor in the source signal. Analogue clipping can only be prevented by reducing the analogue signal
gain or by adjusting the source signal.
QUICK RELEASE CONTROL
The DRC includes a Quick-Release feature to handle short transient peaks that are not related to the
intended source signal. The Quick Release feature ensures that these transients do not cause the
intended signal to be masked by the longer time constants of DRC_DCY.
The Quick-Release feature is enabled by setting the DRC_QR bit. When this bit is enabled, the DRC
measures the crest factor (peak to RMS ratio) of the input signal. A high crest factor is indicative of a
transient peak that may not be related to the intended source signal. If the crest factor exceeds the
level set by DRC_QR_THR, then the normal decay rate (DRC_DCY) is ignored and a faster decay
rate (DRC_QR_DCY) is used instead.
The DRC Quick-Release control bits are described in Table 16.
Table 16 DRC Quick-Release Control
INITIALISATION
When the DRC is initialised, the gain is set to the level determined by the DRC_STARTUP_GAIN
register field. The default setting is 0dB, but values from -3dB to +6dB are available, as described in
Table 17.
R32 (20h)
DRC 1
R33 (21h)
DRC 2
R32 (20h)
DRC 1
REGISTER
REGISTER
ADDRESS
ADDRESS
10:6
BIT
BIT
7:6
5:4
2
DRC_STARTUP_
GAIN [4:0]
DRC_QR
DRC_QR_THR
[1:0]
DRC_QR_DCY
[1:0]
LABEL
LABEL
DEFAULT
DEFAULT
0_0110
00
00
1
Quick release enable
0 = Disabled
1 = Enabled
Quick release crest factor threshold
00 = 12dB (default)
01 = 18dB
10 = 24dB
11 = 30dB
Quick release decay rate
(seconds/6dB)
00 = 0.725ms (default)
01 = 1.45ms
10 = 5.8ms
11 = Reserved
Initial gain at DRC startup
00000 = -3dB
00001 = -2.5dB
00010 = -2dB
00011 = -1.5dB
00100 = -1dB
00101 = -0.5dB
00110 = 0dB (default)
00111 = 0.5dB
DESCRIPTION
DESCRIPTION
PP, Rev 3.0, April 2009
WM9081
37