WM8978 Wolfson Microelectronics Ltd., WM8978 Datasheet - Page 32

• Manufacturer Part Number: WM8978
• Description: The WM8978 is a low power, high quality stereo codec designed for portable applications such as Digital still camera or Digital Camcorde
• Manufacturer: Wolfson Microelectronics Ltd.

WM8978
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AUXILLIARY INPUTS
INPUT BOOST
Figure 16 Input Boost Stage
Table 9 Input BOOST Stage Control
There are two auxilliary 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.
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 16.
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).
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.
R47
Left Input
BOOST
control
R48
Right Input
BOOST
control
REGISTER
ADDRESS
8
8
BIT
PGABOOSTL
PGABOOSTR
LABEL
1
1
DEFAULT
PGA:
0 = PGA output has +0dB gain
through input BOOST stage.
1 = PGA output has +20dB gain
through input BOOST stage.
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.
Boost enable for left channel input
PTD Rev 2.6 November 2005
DESCRIPTION
Preliminary Technical Data
32