TH72036 Datasheet, PDF (3/16 Pages) Melexis Microelectronic Systems – 868/915MHz FSK/ASK Transmitter

TH72036
868/915MHz
FSK/ASK Transmitter
1 Theory of Operation
1.1 General
As depicted in Fig.1, the TH72036 transmitter consists of a fully integrated voltage-controlled oscillator
(VCO), a divide-by-32 divider (div32), a phase-frequency detector (PFD) and a charge pump (CP). An inter-
nal loop filter determines the dynamic behavior of the PLL and suppresses reference spurious signals. A
Colpitts crystal oscillator (XOSC) is used as the reference oscillator of a phase-locked loop (PLL) synthe-
sizer. The VCO’s output signal feeds the power amplifier (PA). The RF signal power P_out can be adjusted in
four steps from P_out = –11 dBm to +9.5 dBm, either by changing the value of resistor RPS or by varying the
voltage V_PS at pin PSEL. The open-collector output (OUT) can be used either to directly drive a loop antenna
or to be matched to a 50Ohm load. Bandgap biasing ensures stable operation of the IC at a power supply
range of 1.95 V to 5.5 V.
1.2
PRELIMINARY ^{Block Diagram}
CKDIV
7
CKOUT
div 8
5 ^{div 32}
PLL
32
VCC
10
ROI
3
PFD
RPS
R1
PSEL
6
ASKDTA
PA
8 _OUT
antenna
matching
network
XTAL
XOSC
XBUF
CP
VCO
mode
control
4
ENTX
FSKSW
CX2
2
CX1
1
9
FSKDTA
VEE
Fig. 1: Block diagram with external components
2 Functional Description
2.1 Crystal Oscillator
A Colpitts crystal oscillator with integrated functional capacitors is used as the reference oscillator for the PLL
synthesizer. The equivalent input capacitance CRO offered by the crystal oscillator input pin ROI is about
18pF. The crystal oscillator is provided with an amplitude control loop in order to have a very stable fre-
quency over the specified supply voltage and temperature range in combination with a short start-up time.
3901072036
Rev. 005
Page 3 of 16
Data Sheet
June/07