WM8978 Wolfson Microelectronics Ltd., WM8978 Datasheet - Page 27
Manufacturer Part Number
The WM8978 is a low power, high quality stereo codec designed for portable applications such as Digital still camera or Digital Camcorde
Wolfson Microelectronics Ltd.
Preliminary Technical Data
INPUT SIGNAL PATH
used. In the case where DSP mode is used, and mono data is being sent, only the signal channel of
mono data is sent.
AUXILIARY ANALOGUE INPUTS
An analogue stereo FM tuner or other auxiliary analogue input can be connected to the Line inputs of
WM8978, and the stereo signal listened to via headphones, or recorded, simultaneously if required.
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.
In differential mode the larger signal should be input to LIP or RIP and the smaller (e.g. noisy ground
connection) should be input to LIN or RIN.
Figure 11 Microphone Input PGA Circuit
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.
PTD Rev 2.6 November 2005