TH7108EFC Melexis Inc, TH7108EFC Datasheet - Page 4

• Manufacturer Part Number: TH7108EFC
• Description: IC XMITTER 868/915MHZ 16-SSOP
• Manufacturer: Melexis Inc

Specifications of TH7108EFC

• Rohs Status: RoHS non-compliant
• Frequency: 850MHz ~ 920MHz
• Applications: Alarm and Security Systems, RKE
• Modulation Or Protocol: ASK, FM, FSK
• Data Rate - Maximum: 40 kbps
• Power - Output: -15dBm ~ 1dBm
• Current - Transmitting: 6.2mA ~ 12.5mA
• Data Interface: PCB, Surface Mount
• Antenna Connector: PCB, Surface Mount
• Voltage - Supply: 2.2 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 16-SSOP
• Features: -
• Memory Size: -
• Other names: TH7108; TH7108EFF

2 Functional Description
2.1 FSK Modulation
A Colpitts crystal oscillator (XOSC) is used as the reference oscillator of a phase-locked loop (PLL) synthe-
sizer. FSK modulation is achieved by pulling the crystal (XTAL) through the data. So a CMOS-compatible
data stream applied at input DATA digitally modulates the XOSC. Two external pulling capacitors CX1 and
CX2 allow the FSK deviation and center frequency to be adjusted independently. At DATA = LOW CX2 is
connected in parallel to CX1 leading to the low-frequency component of the FSK spectrum (f
DATA = HIGH CX2 is deactivated and the XOSC is set to its high frequency, leading to f
An external reference signal can be directly AC-coupled to pin RO1. Then the TH7108 is used without an
XTAL. The reference signal has to contain the FSK (or FM) and sets the carrier frequency.
2.2 Frequency Modulation
For FM operation an external varactor is required. It simply acts as a pulling capacitor connected in series to
the crystal. Then the analog modulation signal, applied through a series resistor, directly modulates the
XOSC.
2.3 ASK Modulation
The TH7108 can be ASK-modulated by applying data directly at pin PS. This turns the PA on and off and
therefore leads to an ASK signal at the output.
2.4 Mode Control Logic
The mode control logic allows four different modes of operation as listed in the following table. The mode
control pins ENCK and ENTX are pulled-down internally. This guarantees that the whole circuit is shut down
if these pins are left floating.
The clock output CKOUT can be used to drive a µC. This output can be activated by the ENCK pin as re-
quired for any specific application. Clock frequency is 1/8 of the reference crystal frequency.
3901007108
Rev. 008
ENCK
0
0
1
1
ENTX
0
1
0
1
clock only
TX only
all OFF
all ON
Mode
Page 4 of 14
TX standby and clock available
TX active and clock available
TX active, no clock available
whole circuit in standby
Description
FSK/FM/ASK Transmitter
max
TH7108
.
868/915MHz
min
Data Sheet
); while at
May/03