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 25
Audio Interface
Two different microphone inputs and two different speaker outputs are supported. The connection can be either
differential or single-ended but using a differential connection in order to reject common mode noise and TDMA
noise is recommended.
Microphone 2 Inputs
The MIC2 inputs are differential ones. They already include the convenient biasing for an electret microphone
(0,5 mA and 2 Volts). This electret microphone can be directly connected on these inputs. The impedance of the
microphone 2 has to be around 2K. These inputs are the standard ones for a handset design while MIC1 inputs
can be connected to an external headset or a hands-free kit.
The gain of MIC2 inputs is internally adjusted. The gain can be tuned from 30dB to 51dB. The connection to the
microphone is direct. The gain can be tuned using the AT+VGR command. See Appendix B: Sourcing Guide for
Connectors and Peripheral Devices.
MIC2N
MIC2P
C1
C1 = 22pF to 100 pF
33 pF recommended
Figure 3-8: Microphone 2 Input
C1 has to be the nearest as possible to the microphone. Microphone manufacturers provide this capacitor
directly soldered on the microphone.
Table 3-19: Microphone 2 Input Pin Description
Signal Pin Number I/O I/O Type* Description
MIC2P 16 I Analog Microphone 2 positive input
MIC2N 18 I Analog Microphone 2 negative input
* See “Table 3-2: Operating Conditions” in section on the 50-pin Connector Description.