User's Manual

35
7 Audio Interfaces
7.1 Audio Interface
The audio interface circuit consists of:
 Stereo audio CODEC
 Dual audio inputs and outputs
 A configurable PCM, I2S or SPDIF interface
NOTE: the S/PDIF interface is not recommended for use at this time due to an issue with the low-
level BlueCore05-MM firmware revision in use by iWRAP. The audio quality suffers because the
left and right channels get out of sync.
Figure 12 outlines the functional blocks of the interface. The CODEC supports stereo playback and
recording of audio signals at multiple sample rates with a resolution of 16-bit. The ADC and the DAC of
the CODEC each contain two independent channels. Any ADC or DAC channel can be run at its own
independent sample rate.
Figure 12: Audio interface
The interface for the digital audio bus shares the same pins as the PCM CODEC interface described in
section 6.3
, which means that each of the audio buses are mutually exclusive in their usage. Table 12
lists these alternative functions.
PCM Interface
SPDIF Interface
I2S Interface
PCM_OUT
SPDIF_OUT
SD_OUT
PCM_IN
SPDIF_IN
SD_IN
PCM_SYNC
WS
PCM_CLK
SCK
Table 12: Alternative functions of the digital audio bus interface on the PCM interface
7.1.1 Audio Input and Output
The audio input circuitry consists of a dual audio input that can be configured to be either single-ended
or fully differential and programmed for either microphone or line input. It has an analogue and digital
programmable gain stage for optimisation of different microphones.
Audio signals are very sensitive to noise caused by the Bluetooth radio and it is highly recommended to
always use fully differential signals.
The audio output circuitry consists of a dual differential class A-B output stage.