BC352239A Datasheet, PDF (94/116 Pages) List of Unclassifed Manufacturers – BlueCore 3-Multimedia External

Device Terminal Descriptions
8.8.24 Microphone Input
The audio-input is intended for use from 1µA@94dB SPL to about 10µA@94dB SPL. With biasing-resistors R1
and R2 equal to 1kΩ, this requires microphones with sensitivity between about –40dBV and –60dBV. The
microphone for each channel should be biased as shown in Figure 8.29.
Microphone Bias
BlueCore3-Multimedia External
R2
C3
R1
C1
AUDIO_IN_P_LEFT
Input
C2
AUDIO_IN_N_LEFT ^Amplifier
C4
+ _MIC1
Figure 8.29: Microphone Biasing (Left Channel Shown)
The input impedance at AUDIO_IN_N_LEFT, AUDIO_IN_P_LEFT, AUDIO_IN_N_RIGHT and
AUDIO_IN_P_RIGHT is typically 20kΩ. C1 and C2 should be 47nF. R1 sets the microphone load impedance and
is normally in a range of 1 to 2 kΩ. R2, C3 and C4 improve the supply rejection by decoupling supply noise from
the microphone. Values should be selected as required in the specification. R2 may be connected to a
convenient supply, in which case the bias network is permanently enabled, or to the AUX_DAC output (which is
ground referenced and so provides good rejection of the supply), which maybe configured to provide bias only
when the microphone is required.
8.8.25 Line Input
If the input gain is set to less than 21dB BlueCore3-Multimedia External automatically selects line input mode. In
this mode the input impedance at AUDIO_IN_N_LEFT, AUDIO_IN_P_LEFT, AUDIO_IN_N_RIGHT and
AUDIO_IN_P_RIGHT are increased to 130kΩ typically. In line-input mode, the full-scale input signal is about
400mV rms. Figure 8.30 and Figure 8.31 show two circuits for line input operation and show connections for
either differential or single ended inputs.
C1
AUDIO_IN_P_LEFT
C2
AUDIO_IN_N_LEFT
Figure 8.30: Differential Input (Left Channel Shown)
C1
AUDIO_IN_P_LEFT
C2
AUDIO_IN_N_LEFT
Figure 8.31: Single Ended Input (Left Channel Shown)
BC352239A-ds-001Pc
© Cambridge Silicon Radio Limited 2004
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