Smart Machine Smart Decision
Figure 32: Speaker with amplifier reference circuit
4.7.3. Audio Electronic Characteristic
Table 15: Microphone input characteristics
Parameter
Min
Typ
Max
Unit
Microphone biasing voltage
1.9
2.2
V
Working current
2.0
mA
Input impedance(differential)
13
20
27
KΩ
Idle channel noise
-67
dBm0
Input level:-40dBm0
29
dB
SINAD
Input level:0dBm0
69
dB
Table 16: Audio output characteristics
Parameter
Conditions
Min
Typ
Max
Unit
R
L
=32 Ω receiver
-
90
-
mW
Normal output
R
L
=8 Ω speaker
-
-
1080
mW
4.7.4. TDD
Audio signal could be interferenced by RF signal. Coupling noise could be filtered by adding 33pF and 10pF
capacitor to audio lines. 33pF capacitor could eliminate noise from GSM850/EGSM900MHz, while 10pF
capacitor could eliminate noise from DCS1800/PCS1900Mhz frequency. Customer should develop this filter
solution according to field test result.
GSM antenna is the key coupling interfering source of TDD noise. Thereat, pay attention to the layout of audio
lines which should be far away from RF cable, antenna and VBAT pin. The bypass capacitor for filtering should
be placed near module and another group needs to be placed near to connector.
Conducting noise is mainly caused by the VBAT drop. If audio PA was powered by VBAT directly, then there
