Telit Wireless Solutions GE863-PY, GE863-QUAD manual Balanced Microphone Biasing

Page 36

GE863-QUAD

GE863-PY

1vv0300715 Rev. 1 - 19/09/06

7.4 Microphone Biasing

The electret microphones usually need a biasing voltage to work properly. Refer to your microphone provider for the characteristics required.

NOTE: The microphones have a hot wire were the positive biasing must be connected. Usually it is indicated by a + symbol or a red point. If the polarity of the bias is reversed, then the microphone will not work properly. For this reason be sure to respect the mic. biasing polarity.

7.4.1 Balanced Microphone Biasing

The balanced microphone bias voltage should be obtained from a dedicated voltage regulator, in order to eliminate the noise present on the power lines. This regulator can be the same for all the audio paths. The microphone should be supplied from a capacitor multiply circuit.

For example a circuit for the balanced microphone biasing can be:

NOTE: In the balanced application the resistors R2 and R3 must have the same value to keep the circuit balanced.

Reproduction forbidden without Telit Communications S.p.A. written authorization - All Right reserved

page 36 of 79

Image 36

Contents GE863-QUAD GE863-PY Hardware User Guide Contents 10.1 10.210.3 10.412.1 13.113.2 This document is relating to the following products Overview GE863 module connections PIN-OUTPin Signal Function Internal Type Pull up Pin Signal Function Internal Type Pins Layout Hardware Commands Turning on the GE863-QUAD/PYTurning OFF the GE863-QUAD/PY Turning off of the device can be done in two waysHardware Unconditional Reboot Hardware shutdownGE863-QUAD Power Supply 1Power Supply RequirementsGE863-QUAD/PY power requirements are 2General Design Rules Electrical design Guidelines1.2 + 12V input Source Power Supply Design Guidelines An example of linear regulator with 5V input isBattery Source Power Supply Design Guidelines An example of switching regulator with 12V input isBattery Charge control Circuitry Design Guidelines Thermal Design Guidelines Power Supply PCB layout Guidelines Antenna GSM Antenna RequirementsGSM Antenna installation Guidelines Serial PortsGSM Antenna PCB line Guidelines Absolute Maximum Ratings -Not Functional Parameter Min Max Level Min MaxSignals in the Uart connector on the EVK are Number Pad Number17-28-36 Ground 45-48-50-56 Clear to Send Output from the GE863-QUAD/PY thatIt is available on the following pins 2MODEM Serial Port 2 Python Debug3RS232 level translation An example of level translation circuitry of this kind is 5V Uart level translation GE863-QUAD Audio Section Overview GM863-GPS Microphone Paths Characteristic and Requirements Echo canceller type HandsetEcho canceller type Car kit hands-free + 20dBThat means You can set GA= +20dB to use standard resistor valuesTIP environment consideration General Design Rules Other considerationsMicrophone Biasing Balanced Microphone BiasingUnbalanced Microphone Biasing GE863-QUAD Microphone Buffering Buffered Balanced MicSample circuit can be Gain = RR604605 = RR607606 Buffer gain is given by the formulaBuffered Unbalanced Single Ended Microphone Freq . = 2π * R719* C726 2π * R711* C727 Buffer bandwidth at -3dB shall be 4KHzGE863-QUAD Output Lines Speaker Short descriptionOutput Lines Characteristics SW volume level step Number of SW volume stepsNoise Filtering Handset Earphone Design Hands-Free Earphone Low Power Design An example of internal Ear amplifier could beCar Kit Speakerphone Design Evaluation Kit for Telit Modules EVK2 Short Description2 EVK2 Audio Lines Characteristics @ 350mWData Integrity ESDSchematic SIM SupplyLayout Using a Gpio Pad as Input Using a Gpio Pad as OutputGeneral Purpose I/O 10.3Using the Alarm Output GPIO6 Using the Buzzer Output GPIO7DAC and ADC section 11.1DAC ConverterDescription Min Max UnitsAn AT command is available to use the DAC function Command is AT#DAC=enable,valueEnabling DAC Low Pass Filter ExampleUsing ADC Converter Input Voltage range AD conversion Bits Resolution11.2ADC Converter Camera 12.1Transchip CameraType Sensitivity LuxCamera Interface Connectors Camera Physical Detail & Connector Camera Socket Connector Camera Board Module Main Block Diagram for supported cameras Schematic Diagrams for supported camera Camera setting shown here are the defaults ones Example usage script for cameraTaking an reading a photo 13.2Module Finishing & Dimensions Mounting the GE863-QUAD / PY on the Application Board13.1General Surface finishing Ni/Au for all test pads Lead-free AlloyRecommended foot print for the application Debug of the GE863 in Production StencilPCB pad Design Solder paste 13.2.6 GE863-QUAD / PY Solder Reflow Following is the recommended solder reflow profileGE863-QUAD Packing System Section A-AModules orientation on tray Moisture Sensibility Conformity Assessment Issues Safety Recommandations Document Change Log Revision Date Changes21/02/06 19/09/06