Data Sheet

Smart Machine Smart Decision

SIM800F_Hardware Design_V1.00 36 2015-07-31

4.8.3 Audio Electronic Characteristics

Table 13: Microphone Input Characteristics

Parameter Min Typ Max Unit

Mic biasing voltage - 1.9 2.2 V

Working Current - - 2.0 mA

Input impedance(differential) 13 20 27 K

Idle channel noise - - -67 dBm0

Input level:-40dBm0 29 - - dB

SINAD

Input level:0dBm0 - 69 - dB

Table 14: Audio Output Characteristics

parameter Conditions Min Typ Max Unit

Normal output R

=32  receiver - 15 90 mW

4.8.4 TDD

Audio signal could be interfered 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 connector.

Conducting noise is mainly caused by the VBAT drop. If the audio PA was powered by VBAT directly, then there

will be some cheep noise from speaker output easily. So it is better to put big capacitors and ferrite beads near

audio PA input.

TDD noise has something to do with GND signal. If GND plane is not good, lots of high-frequency noises will

interference microphone and speaker over bypass capacitor. So a good GND during PCB layout could avoid

TDD noise.

4.9 SIM Card Interface

4.9.1 SIM Card Application

The SIM interface complies with the GSM Phase 1 specification and the new GSM Phase 2+ specification for

FAST 64 kbps SIM card. Both 1.8V and 3.0V SIM card are supported.