TH72001_12 Datasheet, PDF (3/20 Pages) Melexis Microelectronic Systems – FSK Transmitter

TH72001
315MHz
FSK Transmitter
1 Theory of Operation
1.1 General
As depicted in Fig.1, the TH72001 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
internal 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)
synthesizer. 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 = –12 dBm to +11 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 2.1 V to 5.5 V.
1.2 Block Diagram
4
ENTX
mode
control
PLL
VCC
6
32
ROI ³
XTAL
XOSC
FSKSW ²
CX2
CX1
1
FSKDTA
XBUF
8
VEE
PFD
CP
VCO
RPS
PSEL
5
PA
low
voltage
detector
7
OUT
antenna
matching
network
Fig. 1: Block diagram with external components
3901072001
Rev. 010
Page 3 of 20
Data Sheet
Jun/12