Pre-Production
WM8959
When driving a handset ear speaker using OUT3 and OUT4 from LOMIX and ROMIX, the required
phase difference may be provided by inverting one of the DAC outputs. Alternatively, the phase
difference can be achieved by mixing Left and Right channels through LOMIX to OUT3 and by
muting OUT4. Similarly, the phase difference can be achieved by mixing Left and Right channels
through ROMIX to OUT4 and by muting OUT3.
Note that a differential output will provide an additional 6dB gain at the output pins. Register bits
OUT3ATTN and OUT4ATTN can be used to compensate for this gain if required.
Fully differential headphone drive is possible between LOUT and OUT3 and between ROUT and
OUT4. Routing LOPGA to OUT3 and ROPGA to OUT4 results in a phase inversion at LOUT with
respect to OUT3 and at ROUT with respect to OUT4. This allows fully differential headset drive, with
greatly improved crosstalk performance, improved bass response, increased noise immunity and
removing the need for large and expensive DC-blocking capacitors.
To ensure fully balanced differential operation, LOUT and OUT3 must be set to the same gain as
each other, and ROUT and OUT4 must be set to the same gain as each other. This is best achieved
by setting OUT3ATTN and OUT4ATTN to 0dB, whilst setting volume controls LOPGAVOL and
LOUTVOL at matching levels and setting volume controls ROPGAVOL and ROUTVOL at matching
levels.
Some example headphone output configurations are shown below.
Figure 31 AC-Coupled Headphone Drive
Figure 32 Capless Mode Headphone Drive
Figure 33 Headphone and Ear Speaker Drive
LINE OUTPUT CONFIGURATIONS
Figure 34 Fully Differential Headphone Drive
The line outputs LON, LOP, RON and ROP are each driven by different output mixers as described
below.
The LOP and ROP pins output a mix of LIN12 input PGA, RIN12 input PGA and either LOMIX or
ROMIX outputs.
The LON output is a mix of ROMIX, LOMIX and a phase-inverted copy of LOP.
The RON output is a mix of LOMIX, ROMIX and a phase-inverted copy of ROP.
Volume control of LOMIX and ROMIX is available in all cases above via LOPGA and ROPGA. An
additional -6dB attenuation option is provided on LOP and ROP outputs.
PP, May 2008, Rev 3.1
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
