WM8978
Production Data
w
PD, Rev 4.5, October 2011
28
AUXILIARY INPUTS
There are two auxiliary inputs, AUXL and AUXR which can be used for a variety of purposes such as
stereo line inputs or as a ‘beep’ input signal to be mixed with the outputs.
The AUXL/R inputs can be used as a line input to the input BOOST stage which has gain adjust of -
12dB to +6dB in 3dB steps (plus off). See the INPUT BOOST section for further details.
The AUXL/R inputs can also be mixed into the output channel mixers, with a gain of -15dB to +6dB
plus off.
In addition the AUXR input can be summed into the Right speaker output path (ROUT2) with a gain
adjust of -15 to +6dB. This allows a ‘beep’ input to be output on the speaker outputs only without
affecting the headphone or lineout signals.
INPUT BOOST
Each of the stereo input PGA stages is followed by an input BOOST circuit. The input BOOST circuit
has 3 selectable inputs: the input microphone PGA output, the AUX amplifier output and the L2/R2
input pin (can be used as a line input, bypassing the input PGA). These three inputs can be mixed
together and have individual gain boost/adjust as shown in Figure 14.
Figure 14 Input Boost Stage
The input PGA paths can have a +20dB boost (PGABOOSTL/R=1) , a 0dB pass through
(PGABOOSTL/R=0) or be completely isolated from the input boost circuit (INPPGAMUTEL/R=1).
REGISTER
ADDRESS
BIT LABEL DEFAULT
DESCRIPTION
R47
Left Input
BOOST
control
8
PGABOOSTL
1
Boost enable for left channel input
PGA:
0 = PGA output has +0dB gain through
input BOOST stage.
1 = PGA output has +20dB gain
through input BOOST stage.
R48
Right Input
BOOST
control
8
PGABOOSTR
1
Boost enable for right channel input
PGA:
0 = PGA output has +0dB gain through
input BOOST stage.
1 = PGA output has +20dB gain
through input BOOST stage.
Table 7 Input BOOST Stage Control
The Auxilliary amplifier path to the BOOST stages is controlled by the AUXL2BOOSTVOL[2:0] and
AUXR2BOOSTVOL[2:0] register bits. When AUXL2BOOSTVOL/AUXR2BOOSTVOL=000 this path
is completely disconnected from the BOOST stage. Settings 001 through to 111 control the gain in
3dB steps from -12dB to +6dB.
The L2/R2 path to the BOOST stage is controlled by the LIP2BOOSTVOL[2:0] and the
RIP2BOOSTVOL[2:0] register bits. When L2_2BOOSTVOL/R2_2BOOSTVOL=000 the L2/R2 input
pin is completely disconnected from the BOOST stage. Settings 001 through to 111 control the gain
in 3dB steps from -12dB to +6dB.
Summary of Contents for WM8978
Page 11: ...Production Data WM8978 w PD Rev 4 5 October 2011 11 SPEAKER OUTPUT THD VERSUS POWER...
Page 14: ...WM8978 Production Data w PD Rev 4 5 October 2011 14 AUDIO PATHS OVERVIEW...
Page 55: ...Production Data WM8978 w PD Rev 4 5 October 2011 55 Figure 26 Left Right Output Channel Mixers...
Page 60: ...WM8978 Production Data w PD Rev 4 5 October 2011 60 Figure 29 Speaker Outputs LOUT2 and ROUT2...