9.2.18 Side Tone
In some applications it is necessary to implement side tone. This side tone function involves feeding a properly
gained microphone signal in to the DAC stream, e.g. earpiece. The side tone routing selects the version of the
microphone signal from before or after the digital gain in the ADC interface and adds it to the output signal before
or after the digital gain of the DAC interface, see Figure 9.8.
G-
T
W
-000
5375.1.1
Side Tone Route
Digital Input
Analogue Output
Digital Output
Analogue Input
Digital Gain
Demux
Mux
DAC
DAC Interface
Side Tone
Digital Gain
ADC
ADC Interface
Side Tone Route
Side Tone Gain
Figure 9.8: Side Tone
The ADC provides simple gain to the side tone data. The gain values range from -32.6dB to 12.0dB in alternating
steps of 2.5dB and 3.5dB, see Table 9.5.
Advance Information
This material is subject to CSR's non-disclosure agreement
© Cambridge Silicon Radio Limited 2011
Page 45 of 110
CS-209182-DSP1
CSR8640 BGA
Data Sheet
