WM8711_06 Datasheet, PDF (18/47 Pages) Wolfson Microelectronics plc – Internet Audio DAC with Integrated Headphone Amplifier

Production Data
WM8711 / WM8711L
DAC
The WM8711/L employs a multi-bit sigma delta oversampling digital to analogue converter. The
scheme for the converter is illustrated in Figure 7.
FROM DAC
DIGITAL
FILTERS
TO LINE OUTPUT
Figure 7 Multi-Bit Oversampling Sigma Delta Schematic
The DAC converts the multi-level digital audio data stream from the DAC digital filters into high quality
analogue audio.
LINE OUTPUTS
The WM8711/L provides two low impedance line outputs LLINEOUT and RLINEOUT, suitable for
driving typical line loads of impedance 10K and capacitance 50pF.
The LLINEOUT and RLINEOUT outputs are only available at a line output level and are not level
adjustable in the analogue domain, having a fixed gain of 0dB. The level is fixed such that at the DAC
full scale level the output level is Vrms at AVDD = 3.3 volts. Note that the DAC full scale level tracks
directly with AVDD. The scheme is shown in Figure 8. The line output includes a low order audio low
pass filter for removing out-of band components from the sigma-delta DAC. Therefore no further
external filtering is required in most applications.
FROM LINE
INPUTS
BYPASS
FROM DAC
DACSEL
VMID
LINEOUT
TO HEADPHONE AMP
Figure 8 Line Output Schematic
The line output is muted by either muting the DAC (analogue) or Soft Muting (digital) and disabling
the BYPASS path. Refer to the DAC section for more details. Whenever the DAC is muted or the
device placed into standby mode the DC voltage is maintained at the line outputs to prevent any
audible clicks from being present.
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PD Rev 4.3 September 2006
18