User Manual

HE863 Family Hardware User Guide
1vv0300891 Rev.6
- 2011-04-14
Reproduction forbidden without Telit Communications S.p.A’s. written authorization - All Rights
Reserved. Page 68 of 92
11.2. Microphone Characteristics
TIP:
Being the microphone circuitry the more noise sensitive, its
design and layout must be realized with particular care. Both
microphone paths are balanced and the OEM circuitry must be
balanced designed to reduce the common mode noise typically
generated on the ground plane. However the customer can use
the unbalanced circuitry for particular application.
11.2.1. Input Lines (MT and HF) Characteristics
Line coupling AC(*)
Line type Balanced/Unbalanced
Coupling capacitor
 100nF
Differential input
impedance
50K
Differential input
voltage
Max 0.8Vpp
input capacitance
5pF(typ.)
(*) WARNING: AC means that the signals from the microphone
have to be connected to input lines of the module through
capacitors which value has to be  100nF, Not respecting this
constraint, the input stages will be damaged.
When particular OEM application needs a Single Ended Input
configuration, it is forbidden connecting the unused input
directly to Ground, but only through a 100nF capacitor. Don’t
forget that thus the useful input signal will be halved.
11.3. OUTPUT LINES (Speaker)
We suggest driving the load differentially from both output
drivers, thus the output swing will double and the need for the
output coupling capacitor avoided.
If a particular OEM application needs a Single Ended Output
configuration the output power will be reduced four times.