Wolfson WM9090, Руководство пользователя

Страница: 50 / 81

WM9090
Production Data
w
PD, November 2010, Rev 4.1
50
REGISTER
ADDRESS
BIT LABEL DEFAULT DESCRIPTION
1:0 DCS_STARTUP_C
OMPLETE [1:0] 00 DC Servo Start-Up status
0 = Start-Up DC Servo mode not
completed.
1 = Start-Up DC Servo mode
complete.
Bit [1] = HPOUT1R
Bit [0] = HPOUT1L
Table 28 DC Servo Enable and Start-Up Modes
DC SERVO ACTIVE MODES
The DC Servo modes described above are suitable for initialising the DC offset correction circuit on
the Headphone outputs as part of a controlled start-up sequence which is executed before the signal
path is fully enabled. Additional modes are available for use whilst the signal path is active; these
modes may be of benefit following a large change in signal gain, which can lead to a change in DC
offset level. Periodic updates may also be desirable to remove slow drifts in DC offset caused by
changes in parameters such as device temperature.
The DC Servo circuit is enabled on HPOUT1L and HPOUT1R by setting DCS_ENA_CHAN_0 and
DCS_ENA_CHAN_1 respectively, as described earlier in Table 28.
Writing a logic 1 to DCS_TRIG_SINGLE_ n initiates a single DC offset measurement and adjustment
to the associated output; (‘n’ = 0 for Left channel, 1 for Right channel). This will adjust the DC offset
correction on the selected channel by no more than 1LSB (0.25mV).
Setting DCS_TIMER_PERIOD_01 to a non-zero value will cause a single DC offset measurement
and adjustment to be scheduled on a periodic basis. Periodic rates ranging from every 0.52s to in
excess of 2hours can be selected.
Writing a logic 1 to DCS_TRIG_SERIES_ n initiates a series of DC offset measurements and applies
the necessary correction to the associated output. The number of DC Servo operations performed is
determined by DCS_SERIES_NO_01. A maximum of 128 operations may be selected, though a
much lower value will be sufficient in most applications.
The DC Servo control fields associated with active modes (suitable for use on a signal path that is in
active use) are described in Table 29.
REGISTER
ADDRESS
BIT LABEL DEFAULT DESCRIPTION
R84 (54h)
DC Servo 0 13 DCS_TRIG_SINGLE
_1 0 Writing 1 to this bit selects a
single DC offset correction for
HPOUT1R.
In readback, a value of 1
indicates that the DC Servo
single correction is in progress.
12 DCS_TRIG_SINGLE
_0 0 Writing 1 to this bit selects a
single DC offset correction for
HPOUT1L.
In readback, a value of 1
indicates that the DC Servo
single correction is in progress.
9 DCS_TRIG_SERIES
_1 0 Writing 1 to this bit selects a
series of DC offset corrections
for HPOUT1R.
In readback, a value of 1
indicates that the DC Servo DAC
Write correction is in progress.