th71081 ETC-unknow, th71081 Datasheet - Page 2

• Manufacturer Part Number: th71081
• Description: 868/915mhz Transmitter Source
• Manufacturer: ETC-unknow

General Description
The TH71081 ASK transmitter IC is designed for
applications in the European 868MHz industrial-
scientific-medical (ISM) band, according to the EN
300 220 telecommunications standard. It can also
be used for any other system with carrier
frequencies ranging from 800 MHz to 930 MHz
(e.g. for applications in the US 915MHz ISM band).
Theory of Operation
General
As depicted in Fig.1, the TH71081 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. An external loop filter at pin LF determines
the dynamic behaviour of the PLL and suppresses
reference spurious signals.
The VCO’s output signal feeds the power amplifier
(PA). RF signal power P
steps from P
changing the value of resistor R
voltage V
differential output (OUT1, OUT2) can be used to
either directly drive a loop antenna or to be
converted to a single-ended impedance by means
of a balanced-to-unbalanced (balun) transformer.
For
differential output should be matched to a load of
approx. 1 k .
Bandgap biasing ensures stable operation of the IC
at a power supply range of 2.2 V to 5.5 V.
ASK Modulation
The TH71081 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.
3901071081
Rev. 004
maximum
PS
at pin PS/DATA. The open-collector
o
= –15 dBm to +1 dBm either by
available
o
can be adjusted in six
output
1
or by varying the
power,
the
Page 2 of 10
LO Source
Many applications require a stable RF source. For
this purpose, the TH71081 can be used without
modulation as an easy-to-use, PLL-stabilized,
continuous wave (CW) generator.
Frequency Modulation (FM)
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.
Mode Control Logic
The mode control logic allows two different modes
of operation as listed in the following table. The
mode control pin ENTX is pulled-down internally.
This guarantees that the whole circuit is shut down
if this pin is left floating.
Table 1: Modes of operation
The transmitter's carrier frequency f
by the frequency of the reference crystal f
used. The integrated PLL synthesizer ensures that
each RF value, ranging from 800 MHz to 930 MHz,
can be achieved by using a crystal with reference
frequency according to: f
the PLL feedback divider ratio.
ENTX
0
1
ASK Transmitter / LO Source
TX disabled whole circuit in standby
TX enable TX active
Mode
ref
= f
TH71081
c
/N, where N = 32 is
Description
868/915MHz
c
is determined
Data Sheet
Dec. 2001
ref
that is