GM862-GPS Hardware User Guide GM862-GPS HW User Guide 1vv0300728 Rev.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 Contents 1 Overview ...........................................................................................................................4 2 Hardware Commands ......................................................................................................5 2.1 Turning ON the GM862-GPS ..................................................................................................5 2.2 Turning OFF the GM862-GPS ..................
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 6.3.1 7 8 6.4 Handset earphone design....................................................................................................42 6.5 Hands-free earphone (low power) design ..........................................................................43 6.6 Car Kit speakerphone design..............................................................................................44 General Purpose I/O....................................
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 1 Overview The aim of this document is the description of some hardware solutions useful for developing a product with the Telit GM862-GPS modules. In this document all the basic functions of a mobile phone will be taken into account; for each one of them a proper hardware solution will be suggested and eventually the wrong solutions and common errors to be avoided will be evidenced.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 2 Hardware Commands 2.1 Turning ON the GM862-GPS To turn on the GM862-GPS the pin ON# must be tied low for at least 1 second and then released. The maximum current that can be drained from the ON# pin is 0,1 mA. A simple circuit to do it is: ON# R1 Q1 Power ON impulse R2 GND NOTE: don't use any pull up resistor on the ON# line, it is internally pulled up.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 For example: 1- Let's assume you need to drive the ON# pin with a totem pole output of a +3/5 V microcontroller (uP_OUT1): 2- Let's assume you need to drive the ON# pin directly with an ON/OFF button: Reproduction forbidden without Telit Communications S.p.A.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 2.2 Turning OFF the GM862-GPS The turning off of the device can be done in two ways: • by software command (see GM862-GPS Software User Guide) • by hardware shutdown When the device is shut down by software command or by hardware shutdown, it issues to the network a detach request that informs the network that the device will not be reachable any more.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 2.2.2 Hardware Unconditional Reboot To unconditionally Reboot the GM862-GPS the pin RESET# must be tied low for at least 200 milliseconds and then released. The maximum current that can be drained from the ON# pin is 0,15 mA. A simple circuit to do it is: RESET# Unconditional Power OFF impulse GND NOTE: don't use any pull up resistor on the RESET# line nor any totem pole digital output.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 For example: 1- Let's assume you need to drive the RESET# pin with a totem pole output of a +3/5 V microcontroller (uP_OUT2): Unconditional Reboot impulse The hardware unconditional reboot must not be used during normal operation of the device since it does not detach the device from the network. It shall be kept as an emergency exit procedure to be done in the rare case that the device gets stacked waiting for some network or SIM responses.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 3 Power Supply The power supply circuitry and board layout are the most important part in the full product design and they strongly reflect on the product overall performances, hence read carefully the requirements and the guidelines that will follow for a proper design. 3.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 3.2 General Design Rules The principal guidelines for the Power Supply Design embrace three different design steps: - the electrical design - the thermal design. - the PCB layout. 3.2.1 Electrical design Guidelines The electrical design of the power supply depends strongly from the power source where this power is drained.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 An example of linear regulator with 5V input is: Reproduction forbidden without Telit Communications S.p.A.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 3.2.1.2 + 12V input Source Power Supply Design Guidelines • • • • • • • The desired output for the power supply is 3.8V, hence due to the big difference between the input source and the desired output, a linear regulator is not suited and shall not be used. A switching power supply will be preferable because of its better efficiency especially with the 2A peak current load represented by the GM862-GPS.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 An example of switching regulator with 12V input is: 3.2.1.3 Battery Source Power Supply Design Guidelines • The desired nominal output for the power supply is 3.8V and the maximum voltage allowed is 4.2V, hence a single 3.7V Li-Ion cell battery type is suited for supplying the power to the Telit GM862-GPS module. The three cells Ni/Cd or Ni/MH 3,6 V Nom.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 3.2.1.4 Battery Charge control Circuitry Design Guidelines The charging process for Li-Ion Batteries can be divided into 4 phases: • Qualification and trickle charging • Fast charge 1 - constant current • Final charge - constant voltage or pulsed charging • Maintenance charge The qualification process consists in a battery voltage measure, indicating roughly its charge status.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 As you can see, the charging process is not a trivial task to be done; moreover all these operations should start only if battery temperature is inside a charging range, usually 5°C - 45°C.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 3.2.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 3.2.3 Power Supply PCB layout Guidelines As seen on the electrical design guidelines the power supply shall have a low ESR capacitor on the output to cut the current peaks and a protection diode on the input to protect the supply from spikes and polarity inversion. The placement of these components is crucial for the correct working of the circuitry. A misplaced component can be useless or can even decrease the power supply performances.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 4 Serial Ports The serial port on the Telit GM862-GPS is the core of the interface between the module and OEM hardware. 2 serial ports are available on the module: • MODEM SERIAL PORT • GPS SERIAL PORT (NMEA) Several configurations can be designed for the serial port on the OEM hardware, but the most common are: - RS232 PC com port - microcontroller UART @ 2.
GM862-GPS Hardware User Guide 1vv0300728 Rev.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 Signal Name Usage RX_GPS GM862GPS Pin Number 41 GPS Transmit line Output line of GPS serial Port (NMEA TX_GPS 35 GPS Receive line Input line of GPS serial Port (NMEA GND 2-4-6-8 Ground ground protocol) protocol) The default configuration is 4800 bps, 8, n, 1 GPS RX Lines and TX lines may need a dual supply isolation buffer like an FXLP34 to avoid CMOS high states while in POWER SAVING. 4.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 An example of level translation circuitry of this kind is: the RS232 serial port lines are usually connected to a DB9 connector with the following layout: Reproduction forbidden without Telit Communications S.p.A.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 4.2 5V UART level translation If the OEM application uses a microcontroller with a serial port (UART) that works at a voltage different from 2.8 - 3V, then a circuitry has to be provided to adapt the different levels of the two set of signals. As for the RS232 translation there are a multitude of single chip translators, but since the translation requires very few components, then also a discrete design can be suited.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 NOTE: The UART input line TXD (rx_uart) of the GM862-GPS is NOT internally pulled up with a resistor, so there may be the need to place an external 47KΩ pull-up resistor, either the DTR (dtr_uart) and RTS (rts_uart) input lines are not pulled up internally, so an external pull-up resistor of 47KΩ may be required. A power source of the internal interface voltage corresponding to the 2.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 5 Audio Section Overview The Base Band Chip of the GM862-GPS Telit Module provides two different audio blocks; both in transmit (Uplink) and in receive (Downlink) direction: “MT lines” should be used for handset function, “HF lines” is suited for hands -free function (car kit). These two blocks can be active only one at a time, selectable by AXE hardware line or by AT command.
50cm 7cm 3,3mV -45dBV/Pa -45dBV/Pa 0,33mV Reproduction forbidden without Telit Communications S.p.A. written authorization - All Right reserved GM862-GPS Audio Paths +10dB +20dB 23mV 365mV rms rms Mic_HF- Mic_HF+ Mic_MT- Mic_MT+ GM862-GPS Ear_HF- Ear_HF+ Ear_MT- Ear_MT+ 16 ended Single Balanced Power Buffers Fully Differential -12dBFS Differential Line-Out Drivers egolite.skd 8 GM862-GPS Hardware User Guide 1vv0300728 Rev.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 5.1 Microphone paths characteristic and requirements TIP: being the microphone circuitry the more noise sensitive , its design and layout must be done with particular care. Both microphone paths are balanced and the OEM circuitry should be balanced designed to reduce the common mode noise typically generated on the ground plane. However also an unbalanced circuitry can be used for particular OEM application needs .
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 TIP: definition of the nominal sensitivity of the microphone lines . The nominal sensitivity of the microphone lines indicates the voltage level on the GM862-GPS pins present during "normal spoken" conditions. For a handset , the "normal spoken” conditions take place when the talker mouth is 7cm far from the microphone ; under these conditions the voice will produce an acoustic pressure of -4,7dBPa @1kHz on the microphone membrane .
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 TIP: environment consideration . For hands-free/car kit microphone, you must take into account the voice attenuation, due to the distance between the microphone itself and the talker , when designing the external microphone amplifier.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 5.2 General Design Rules There are several configurations for the audio paths, but the most effective difference is between balanced and unbalanced microphone configuration. It is highly recommended to keep the whole microphone path balanced even if this means having 2 wires connecting the microphone instead of one needed (plus ground) in the unbalanced case.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 5.4 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. 5.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 NOTE: The cable to the microphone should not be shielded, instead a twisted pair cable shall be used. NOTE: The microphone sensitivity changes with the value of R2 and R3. Usually the microphones are characterized with 2kΩ biasing resistance, so try to keep the sum of R2 and R3 around 2kΩ. Refer to your microphone manufacturer for the mic. characteristics. 5.4.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 NOTE: In the unbalanced application the capacitor C3 shall be > 200nF otherwise the frequency response will be cut at low band frequencies (down to 300Hz). This capacitor can be placed close to the MIC- pad (MIC_HF- or MIC_MT- depending on the audio path chosen) or if possible it should be placed close to the shielded cable connector.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 5.5 Microphone buffering As seen previously, a microphone shall be connected to the input pins of the GM862-GPS through a buffer amplifier that boosts the signal level to the required value. Again the buffered microphone circuitry can be balanced or unbalanced: where possible it is always preferable a balanced solution. The buffering circuit shall be placed close to the microphone or close to the microphone wire connector. 5.5.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 The buffer gain is given by the formula: Gain = R604 R606 = R605 R607 The C636 and C637 capacitors are placed in order to cut off the gain at higher frequencies than the transmitted GSM band, the cutoff frequency (-3dB) should be 3500Hz in order to have -1dB at 3kHz. The cutoff frequency is given by the formula: freq. = 1 1 = [Hz] 2π * R604 * C 637 2π * R606 * C 636 TIP: example of calculation .
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 5.5.2 Buffered Unbalanced (Single Ended) Microphone . 2,7nF 6,8nF The above schematic can be used for a single ended (buffered unbalanced) microphone ; the required biasing circuitry is not included. Note also that the capacitor C3 is not needed .
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 The buffer bandwidth at -3dB shall be 4KHz. Note that the biasing of the operational amplifier is given for the inverting amplifier by the series divider R714-R715. The 100nF capacitor C719 is needed to filter the noise that could be coupled to that divider. For the not inverting operational amplifier the biasing is given by a different divider R715-R717 with the capacitor C720 and through a series resistor R718 of 470KΩ.
GM862-GPS Hardware User Guide C726= 1/ (2π*4000*R719)= 7.10 *10 -9 F 1vv0300728 Rev. 0 - 27/04/06 C727= 1/ (2π*4000*R711)= 2,65 *10 -9 F modified in 6,8nF (fc1=4181Hz ) and 2,7nF (fc2=3931Hz) because of commercial values . Reproduction forbidden without Telit Communications S.p.A.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 6 OUTPUT LINES (Speaker) 6.1 Short description. The Telit GM862-GPS provides two audio paths in receive section. Only one of the two paths can be active at a time, selectable by AXE hardware line or by AT command.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 6.2 Output lines characteristics . “Ear_MT” Differential Line-out Drivers Path • line coupling: • line type: • output load resistance : • internal output resistance: • signal bandwidth: • max.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 6.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 6.4 Handset earphone design As seen previously, a 16Ω earpiece can be directly connected to the output pads EAR_MT+ and EAR_MT- of the GM862-GPS. This solution is often the more cost effective, reducing the components count to a minimum.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 The resulting gain and high pass cut can be obtained with the formula: Gain = freq. = R3 R2 1 [Hz] 2π * R3 * C 4 And an example of internal Ear amplifier could be : +12dB GM862-GPS Some amplifier require a low impedance load at high frequency in order to avoid auto oscillation, this can be made with a capacitor (100nF) in series with a resistor (15Ω).
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 6.6 Car Kit speakerphone design For the car kit speaker phone function the power output requirement is usually at least 4W, therefore an amplifier is needed to boost the GM862-GPS output. The design of the amplifier shall comply with the following guidelines: • • • • • • The input to the amplifier MUST be taken from the “Ear_HF” audio path of the GM862-GPS, because of its echo canceller parameters suited to a car cabin use.
GM862-GPS Hardware User Guide 1vv0300728 Rev.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 7.3 Using the Alarm Output GPIO6 The GPIO6 pin, when configured as Alarm Output, is controlled by the GM862-GPS module and will rise when the alarm starts and fall after the issue of a dedicated AT command.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 8 GPS Receiver 8.1 GPS Antenna The GE863-GPS module is not provided with an internal LNA amplifier. The use of an active antenna is suggested to achieve a good performance. The module is provided of an Antenna supply circuit with the following characteristics: • Supply voltage referred to VBATT (mandatory a working range between 3.4 to 4.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 9 Camera 9.1 Camera Transchip The GM862-GPS provides a direct support for Transchip digital cameras with the following characteristics: Type: Technology: Max picture size: Output format: Sensitivity: TRANSCHIP TC5747 CMOS COLOR camera VGA 480x640 pixels landscape JPEG 4 Lux 9.1.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 50 47 2-4-6 32 2-4-6 n.c 13 DOUT_6 I/O n.c 14 DOUT_7 I/O n.c 15 DOUT_8 I/O n.c 16 VCLKOUT O n.c 17 VALIDH O n.c 18 VALIDV O 19 DVDD28 I 20 SDIN I/O Ground 21 PS1 I Camera power type selector 22 PS2 I Ground 23 SHIELD - Flash Enable 24 LED_CTRL O GPIO7 CAM_PWR_ON GPIO4 IICSDA_CAM GND GPIO8 PD(0) GND O External 2.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 Camera Socket Connector 9.1.3 Reproduction forbidden without Telit Communications S.p.A.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 EVB for Transchip camera support In order to interface the Telit GM862 with a CMOS camera, Telit has developed an evaluation board. The EVK allow connecting all Telit modules through 2 connectors of 40 pins each. The I2CBUS DUAL CAMERA board is plugged in the 2 connectors of 30 pins each on the module board. CAMERA BOARD MODULE BOARD MAIN BOARD Reproduction forbidden without Telit Communications S.p.A.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 9.1.4 Block Diagram for supported camera DVDD is an external power supply of 2.8V, controlled or gated by pin CAM_PWR_ON. CAMERA TRANSCHIP PD[6] GND AVDD PD[1] CAM_CLK GND DVDD AVDD GND DVDD IICSDA_CAM GND PD[0] GND MON1_CAM 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 CAM_CLK Reproduction forbidden without Telit Communications S.p.A.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 9.1.5 Schematic Diagrams for supported cameras Reproduction forbidden without Telit Communications S.p.A.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 9.1.
GM862-GPS Hardware User Guide 1vv0300728 Rev. 0 - 27/04/06 10 Document Change Log Revision ISSUE#0 Date 27/04/06 Changes Release First ISSUE# 0 Reproduction forbidden without Telit Communications S.p.A.
