Specifications

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Figure 20: Single ended input (left channel shown)
7.2.6 Output Stage
The output digital circuitry converts the signal from 16-bit per sample, linear PCM of
variable sampling frequency to a 2Mbits/s 5-bit multi-bit bit stream, which is fed into the
analogue output circuitry.
The output circuit is comprised of a digital to analogue converter with gain setting and an
output amplifier. Its class AB output stage is capable of driving a signal on both channels
of up to 2V pk-pk differential into a load of 16Ω. The output is available as a differential
signal between AUDIO_OUT_N_LEFT and AUDIO_OUT_P_LEFT for the left channel, as
Figure 20 shows; and between AUDIO_OUT_N_RIGHT and AUDIO_OUT_P_RIGHT for the
right channel. The output is capable of driving a speaker directly if its impedance is at
least 8Ω at reduced output swing and if only one channel is connected or an external
regulator is used.
Figure 21: Speaker output (left channel shown)
The analogue gain of the output stage is controlled by a 3-bit programmable resistive
divider, which sets the gain in steps of approximately 3dB.
The multi-bit bit stream from the digital circuitry is low pass filtered by a third order filter
with a pole at 20kHz. The signal is then amplified in the fully differential output stage,
which has a gain bandwidth of typically 1MHz.
7.2.6.1 Mono Operation
Mono operation is a single-channel operation of the stereo CODEC. The left channel
represents the single mono channel for audio in and audio out. In mono operation, the
right channel is an auxilliary mono channel that may be used in dual mono channel
operation. See section 6.2 for an important note on stereo and mono definitions.
With single mono, the power consumption can be reduced by disabling the other channel.
7.2.6.2 Side Tone
In some applications, it is necessary to implement a side tone. This involves feeding an
attenuated version of the microphone signal to the earpiece. The BlueCore5.Multimedia