WM8978 Datasheet, PDF (17/78 Pages) Wolfson Microelectronics plc – STEREO CODEC WITH SPEAKER DRIVER

Product Preview
WM8978
INPUT SIGNAL PATH
The WM8978 has a number of flexible analogue inputs. There are two input channels, Left and
Right, each of which consists of an input PGA stage followed by a boost/mix stage which drives into
the hi-fi ADC. Each input path has three input pins which can be configured in a variety of ways to
accommodate single-ended, differential or dual differential microphones. There are two auxiliary
input pins which can be fed into to the input boost/mix stage as well as driving into the output path.
A bypass path exists from the output of the boost/mix stage into the output left/right mixers.
MICROPHONE INPUTS
The WM8978 can accommodate a variety of microphone configurations including single ended and
differential inputs. The inputs to the left differential input PGA are LIN, LIP and L2. The inputs to the
right differential input PGA are RIN, RIP and R2.
In single-ended microphone input configuration the microphone signal should be input to LIN or RIN
and the internal NOR gate configured to clamp the non-inverting input of the input PGA to VMID.
Figure 6 Microphone Input PGA Circuit
w
PP Rev 1.7 January 2005
17