GE863 Datasheet, PDF (34/69 Pages) List of Unclassifed Manufacturers – Telit GE863-QUAD / GE863-PY Hardware User guide

Telit GE863-QUAD / GE863-PY
Hardware User guide
1vv0300697, Rev. ISSUE#0, - 21/11/05
6.4.2 Buffered Unbalanced (Single Ended) Mic.
A sample schematic for a buffered unbalanced (single ended) microphone can be:
The schematic does not include the required mic. biasing circuitry. For the biasing the same
circuit as seen before can be used; to be noticed that the capacitor C3 on the unbalanced biasing
circuit is not anymore needed if this Buffered design is used.
Two different configurations are used, one inverting and the other not inverting, hence an
additional +6dB (2 times) gain is achieved by doubling the mic. signal path.
The gain of the not inverting buffer is given by the formula:
Gain = 1+ ^R719
R720
and hence it cannot be less than 1. In the example shown the gain of the not inverting buffer is
1,5 (4dB).
While the gain of the inverting buffer is given by the formula:
Gain = ^R711
R708
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