WM8731 datasheet(18/56 Pages) WOLFSON

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WM8731

Advanced Information

WOLFSON MICROELECTRONICS LTD

AI Rev 2.0 February 2001

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.

12.5k

VMID

LINEIN

ADC

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.

WM8731 데이터시트(PDF) 18 Page - Wolfson Microelectronics plc