xE922-3GR Hardware User Guide
1VV0301272
Rev.0.8 2017-01-05
Reproduction forbidden without written authorization from Telit Communications S.p.A. - All Rights
Reserved.
Page 88 of 112
Parameters headset:
Parameter
Min
Typ
Max
Unit
condition
BW
20
Hz
Lower limit
4
20
kHz
Upper limit
Freq response
-0.5
0.5
dB
20 dB FS ref ampl @997Hz
DR
85
90
dB FS
CCIR
RL=16 ohm, gain +6dB
THD+N
-50
-60
dB
RL=16 ohm, gain +6dB, ref signal -10 dB FS
Vout
2.4
Vpp
RL= 32 ohm, ground-centered
2.0
Vpp
RL= 16 ohm, ground-centered
R_load
14
ohm
Gain
-9.1
6
dB
15.1.2.3.
Loudspeaker
ClassD amplifier driving a typical load of 8 ohm.
Output stage directly connected to V_BAT, as such max output power depending on V_BAT level, common
mode level = V_BAT/2.
Switching frequency is about 1.2MHz by default, but can be fine-tuned.
For this frequency and the higher harmonics an external filtering has to be applied which could be inherently
done with the connected loudspeaker as well.
Fine tuning allows interference reduction. That means the higher harmonics of the switching frequency can be
moved into areas where the interference with other system components is minimized, and on the other side the
optimum efficiency for the amplifier can be adjusted. If for example interference between the class-D
amplifier switching frequency and the RF-TX carrier is observed, the higher harmonics can be moved to be
exactly on the RF-TX carrier frequency. That would hide the class-D amplifier harmonics. For a RF-RX slot
the higher harmonics can be moved to a different frequency, so that the RF-RX channel is in the middle
between two of the higher harmonic spurs of the class-D amplifier.