WM8978_06 Wolfson Microelectronics Ltd., WM8978_06 Datasheet - Page 90

• Manufacturer Part Number: WM8978_06
• Description: Stereo Codec With Speaker Driver
• Manufacturer: Wolfson Microelectronics Ltd.

WM8978
POWER MANAGEMENT
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SAVING POWER BY REDUCING OVERSAMPLING RATE
Table 67 ADC and DAC Oversampling Rate Selection
VMID
Table 68 VMID Impedance Control
BIASEN
Table 69 Analogue Bias Control
The default mode of operation of the ADC and DAC digital filters is in 64x oversampling mode.
Under the control of ADCOSR and DACOSR the oversampling rate may be doubled. 64x
oversampling results in a slight decrease in noise performance compared to 128x but lowers the
power consumption of the device.
The analogue circuitry will not work when VMID is disabled (VMIDSEL[1:0] = 00b). The impedance
of the VMID resistor string, together with the decoupling capacitor on the VMID pin will determine the
startup time of the VMID circuit.
The analogue amplifiers will not operate unless BIASEN is enabled.
R10
DAC control
R14
ADC control
R1
Power
management 1
R1
Power
management 1
REGISTER
ADDRESS
REGISTER
REGISTER
ADDRESS
ADDRESS
3
3
1:0
3
BIT
BIT
BIT
VMIDSEL
BIASEN
LABEL
LABEL
DACOSR128
ADCOSR128
LABEL
0
DEFAULT
00
DEFAULT
DEFAULT
Analogue amplifier bias control
0=disabled
1=enabled
0
0
Reference string impedance to VMID pin
(detemines startup time):
00=off (open circuit)
01=75kΩ
10=300kΩ
11=5kΩ (for fastest startup)
DAC oversample rate select
0 = 64x (lowest power)
1 = 128x (best SNR)
ADC oversample rate select
0 = 64x (lowest power)
1 = 128x (best SNR)
DESCRIPTION
DESCRIPTION
DESCRIPTION
PP Rev 3.0 May 2006
Pre-Production
90