WM8731 Wolfson Microelectronics Ltd., WM8731 Datasheet - Page 19

• Manufacturer Part Number: WM8731
• Description: WM8731 : Low Power Audio Codec With Integrated Headphone Driver
• Manufacturer: Wolfson Microelectronics Ltd.

WM8731
AUDIO SIGNAL PATH
LINE INPUTS
The WM8731 provides Left and Right channel line inputs (RLINEIN and LLINEIN). The inputs are
high impedance and low capacitance, thus ideally suited to receiving line level signals from external
hi-fi or audio equipment.
Both line inputs include independent programmable volume level adjustments and ADC input mute.
The scheme is illustrated in Figure 9. Passive RF and active Anti-Alias filters are also incorporated
within the line inputs. These prevent high frequencies aliasing into the audio band or otherwise
degrading performance.
Figure 9 Line Input Schematic
The gain between the line inputs and the ADC is logarithmically adjustable from +12dB to –34.5dB in
1.5dB steps under software control. The ADC Full Scale input is 1.0V rms at AVDD = 3.3 volts. Any
voltage greater than full scale will possibly overload the ADC and cause distortion. Note that the full
scale input tracks directly with AVDD. The gain is independently adjustable on both Right and Left
Line Inputs. However, by setting the INBOTH bit whilst programming the volume control, both
channels are simultaneously updated with the same value. Use of INBOTH reduces the required
number of software writes required. The line inputs to the ADC can be muted in the analogue domain
under software control. The software control registers are shown Table 2. Note that the Line Input
Mute only mutes the input to the ADC, this will still allow the Line Input signal to pass to the line
output in Bypass Mode.
LINEIN
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VMID
AI Rev 2.3 August 2001
Advanced Information
ADC
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