hardware design v1.00
Table Of Contents
- Contents
- Version History
- 1 Introduction
- 2 SIM968 Overview
- 3 Package Information
- 4 GSM Application Interface
- 4.1 GSM Power Supply
- 4.2 Power on/down Scenarios
- 4.3 Power Saving Mode
- 4.4 Charging Interface
- 4.5 RTC Backup
- 4.6 Serial Interfaces
- 4.7 Audio Interfaces
- 4.8 SIM Card Interface
- 4.9 LCD Display/SPI Interface
- 4.10 Keypad Interface
- 4.11 ADC
- 4.12 RI Behaviors
- 4.13 Network Status Indication
- 4.14 General Purpose Input/Output (GPIO)
- 4.15 External Reset
- 4.16 PWM
- 4.17 I2C Bus
- 4.18 GSM Antenna Interface
- 5 GNSS Application Interface
- 6 Electrical, Reliability and Radio Characteristics
- 6.1 Absolute Maximum Ratings
- 6.2 Recommended Operating Conditions
- 6.3 Digital Interface Characteristics
- 6.4 SIM Card Interface Characteristics
- 6.5 VDD_EXT Characteristics
- 6.6 SIM_VDD Characteristics
- 6.7 VRTC Characteristics
- 6.8 Current Consumption (VBAT = 3.8V)
- 6.9 Electro-Static Discharge
- 6.10 Radio Characteristics
- 6.11 Module label information
- Appendix
Smart Machine Smart Decision
SIM968_Hardware Design_V1.00 2013.02.25
47
but once again, proper testing in an anechoic chamber is a mandatory requirement. These ceramic elements will
need to be located near the end of the ground plane, and will require several millimeters of clearance between the
closest component. It is important to note that use of a LP antenna will result in a minimum of 3dB of gain loss
when compared to a RHCP antenna at a defined elevation. This is due to the right hand gain rule of antenna
propagation.
Use of PIFA antenna is another LP possibility, but the PIFA usually exhibits a considerable amount of gain nulls,
or “holes” in the radiation pattern. This will be undesirable for obtaining a low circular error probability (CEP),
since the antenna may not allow the receiver to capture the desired satellite at the ideal orientation due to these
noted gain nulls. Once again, careful testing in an appropriate anechoic chamber is required.
If the customer’s design is for automotive applications, then an active antenna can be used and located on top of
the car in order for guarantee the best signal quality. GNSS antenna choice should be based on the designing
product and other conditions.
For detailed Antenna designing consideration, please refer to related antenna vendor’s design recommendation.
The antenna vendor will offer further technical support and tune their antenna characteristic to achieve successful
GNSS reception performance depending on the customer’s design.
5.5.3 Active antenna supervisor
SIM968 Technology provides the means to implement an active antenna supervisor with a minimal number of
parts. The antenna supervisor is highly configurable to suit various different applications.
Note: The standard firmware does not support active antenna supervisor. If user wants this function, the firmware must be
customized. Please contact SIMCom for more details.
5.5.3.1 Short circuit Detection
If a short circuit in the active antenna pulls GPS_VANT_IN to ground, then the module will detect it, and the
module will report $GPTXT,01,01,02,ANTSTATUS=SHORT*6D sentence through the serial port. The customer
should check short circuit.
NOTE: The antenna supply voltage is not derived from GPS_VANT_OUT.
5.5.3.2 Open circuit Detection
Firmware supports an active antenna supervisor circuit, which is connected to the pin AADET_N. An example of
an open circuit detection circuit is shown in Figure 11and Figure 12.
High (2.85V level) on AADET_N means that an external antenna is not connected, and the module will report
$GPTXT,01,01,02,ANTSTATUS=OPEN*2B sentence through the serial port. Low on AADET_N means that an
external antenna is connected, and the module will report $GPTXT,01,01,02,ANTSTATUS=OK*3B sentence
through the serial port.