Microphone Interfaces Configuration; Audio Electronic Characteristic; Tdd - SimCom SIM800L Hardware Design

4.7.2.

Microphone Interfaces Configuration

MIC1P/2P
MIC1N/2N
Module
4.7.3.

Audio Electronic Characteristic

Table 15: Microphone input characteristics
Parameter
Microphone biasing voltage
Working current
Input impedance(differential)
Idle channel noise
Input level:-40dBm0
SINAD
Input level:0dBm0
Table 16: Audio output characteristics
Parameter Conditions
R =32 Ω receiver
L
Normal output
R =8 Ω speaker
L
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
SIM800L(MT6261)_Hardware Design_V1.01
The lines in bold type should
be accorded to differential
signal layout rules
Figure 31: Speaker with amplifier reference circuit
Min
13
29
Min
-
-
Smart Machine Smart Decision
These components should
be placed to microphone
as close as possible
ESD
33pF
10pF
33pF
10pF
ESD
33pF
10pF
Typ Max
1.9 2.2
2.0
20 27
-67
69
Typ Max
90 -
- 1080
35
Electret
Microphone
Unit
V
mA
KΩ
dBm0
dB
dB
Unit
mW
mW
2016-07-07