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UC864-G Hardware User Guide
DRAFT
- 29/10/07
Reproduction forbidden without Telit Communications S.p.A. written authorization - All Rights Reserved
page 44 of 66
10.5 Microphone Buffering
As seen previously, a microphone shall be connected to the input pins of UC864-G through a buffer
amplifier that boosts the signal level to the required value.
Again the buffered microphone circuitry can be balanced or unbalanced: where possible it is always
preferable a balanced solution. The buffering circuit shall be placed close to the microphone or close
to the microphone wire connector.
10.5.1 Buffered Balanced Mic
A sample circuit can be:
This circuit has a gain of 10 times (+20 dB), and is therefore suited for the “
Mic_MT
“ input if you have
a microphone with a sensitivity close to the suggested one
(-45 dBV
rms/
Pa
). If your microphone has a
different sensitivity or if the buffer is connected to the “
Mic_HF
“ inputs, then a gain adjustment shall
be done by changing resistors R604 and R606 ( if the required value is not a standard one , you can
change R605 and R607 ) and as a consequence the capacitors C636 and C637 to maintain the
bandwidth 150-4000Hz (at -3dB).
270pF
270pF
+20dB
15K
15K
to
GE863