WM8945
Production Data
INPUT PGA ENABLE
The input PGA (Programmable Gain Amplifiers) is enabled using the register bit INPPGAL_ENA, as
described in Table 1.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R2 (02h)
INPPGAL_ENA
Left Input PGA Enable
0 = Disabled
12
0
Power
Management 1
1 = Enabled
Table 1 Input PGA Enable
To enable the input PGA, the reference voltage VMID and the bias current must also be enabled. See
“Reference Voltages and Master Bias” for details of the associated controls VMID_SEL and
BIAS_ENA.
INPUT PGA CONFIGURATION
Microphone and Line level audio inputs can be connected to the WM8945 in single-ended or
differential configurations. (These two configurations are illustrated in Figure 61 and Figure 62 in the
section describing the external components requirements – see “Applications Information”.)
For single-ended microphone inputs, the microphone signal is connected to the non-inverting input of
the PGA, whilst the inverting input of the PGA is connected to VMID. For differential microphone
inputs, the non-inverted microphone signal is connected to the non-inverting input of the PGA, whilst
the inverted (or ‘noisy ground’) signal is connected to the inverting input pin.
Line level inputs are connected in the same way as a single-ended microphone signal.
The non-inverting input of the PGA is configured using the P_PGAL_SEL register. This register allows
the selection of three possible input pins to the PGA. When the AUX1 or AUX2 pin is used as an
audio input, that pin must be configured for audio using the AUX1_AUDIO or AUX2_AUDIO register
bits.
The inverting input of the PGA is configured using MICLN_TO_N_PGAL. This register allows the PGA
to operate in either single-ended or pseudo-differential configuration.
The registers for configuring the Input PGA are described in Table 2.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R39 (27h)
Input Ctrl
AUX2_AUDIO
AUX2 pin configuration
0 = Non-Audio signal
8
0
1 = AC-coupled Audio signal
AUX1 pin configuration
0 = Non-Audio signal
AUX1_AUDIO
7
4
0
1
1 = AC-coupled Audio signal
MICLN_TO_N_
PGAL
Left Input PGA Inverting Input
Select
0 = Connected to VMID
1 = Connected to IN2L
P_PGAL_SEL
[1:0]
Left Input PGA Non-Inverting Input
Select
1:0
01
00 = Connected to IN2L
01 = Connected to IN1L
10 = Connected to AUX1
11 = Reserved
Table 2 Input PGA Configuration
PD, May 2011, Rev 4.1
24
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
