User's Manual
Table Of Contents
- Introduction
- General Characteristics
- Feature Details
- Feature Descriptions
- Applications
- Mechanical Design Overview
- Mechanical Dimensions
- Climatic and Mechanical Environment Testing Compliance
- Introduction
- 50-Pin Connector Interfaces
- Flashing LED
- SIM Interface
- RF Interface
- DTE/DCE Interface Rates
- Serial Test/Demo Board Components
- Serial Test/Demo Board Block Diagram
- General Guidelines for the Use of the ModemModule
- Reference Documents
- Related Manuals
- Additional Information
- Safety Precautions
- Regulatory Standards Compliance
- Where to Find SMD Connectors
- GSM Antenna
- SIM Card Holder
- LIST OF TABLES
Chapter 3 – Electrical Characteristics
Wireless ModemModule MTMMC-G-F1 and MTMMC-G-F2 Developer’s Guide 26
Microphone 1 Inputs
The MIC1 inputs are differential and do not include internal bias. To use these inputs with an electret
microphone, bias has to be generated outside the ModemModule according to the characteristic of this electret
microphone. These inputs are the standard ones used for an external headset or a hands-free kit. When using a
single-ended connection, be sure to have a very good ground plane, a very good filtering as well as shielding in
order to avoid any disturbance on the audio path. The gain of MIC1 inputs is internally adjusted. The gain can be
tuned from 30dB to 51dB.
The gain can be tuned using the AT+VGR command.
C1
C2
R1
R2
R3
R4
Vcc analog power supply
2.8 V
MIC1P
MIC1N
Differential Connection
Figure 3-9: Microphone 1 Input
R1 = R4 = from 100 to 330 .
R2 = R3 = usually between 1K and 3.3K as per the
microphone characteristics
C1 = 22pF to 100pF
C2 = 47µF
R1 and R4 are used as a voltage supply filter with C2.
C1 has to be the nearest possible to the microphone. Microphone manufacturers provide this capacitor directly
soldered on the microphone.
Table 3-20: Microphone 1 Input Pin Description
Signal Pin Number I/O I/O Type* Description
MIC1P 20 I Analog Microphone 1 positive input
MIC1N 22 I Analog Microphone 1 negative input
* See “Table 3-2: Operating Conditions” in section on the 50-pin Connector Description.