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LO Source. TH71071 Datasheet |
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TH71071
315/433MHz
ASK Transmitter / LO Source
Features
! Fully integrated, PLL-stabilized VCO
! Flexible frequency range from 310 MHz to 450 MHz
! ASK achieved by on/off keying of internal
power amplifier
! FM possible with external varactor
! Wide power supply range from 2.2 V to 5.5 V
! High over-all frequency accuracy
! Very low standby current
! Adjustable output power range from
-12 dBm to +2 dBm
! Adjustable current consumption from
4.8 mA to 11.5 mA
! Differential output well-suited for loop
antenna
! Conforms to EN 300 220 and similar
standard
Ordering Information
Part No.
TH71071
Temperature Range
-40 C° to 85 °C
Package
SOIC8
Application Examples
! Keyless car and central locking
! Low-power telemetry
! Alarm and security systems
! General digital data transmission
! General analog audio signal transmission
! Local oscillator signal generation
Pin Description
LF 1
RO 2
ENTX 3
PS/DATA 4
TH71071
8 VEE
7 OUT1
6 OUT2
5 VCC
3901071071
Rev. 004
Page 1 of 10
Data Sheet
Dec. 2001
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TH71071
315/433MHz
ASK Transmitter / LO Source
General Description
The TH71071 ASK transmitter IC is designed for
applications in the European 433MHz 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 310 MHz to 450 MHz
(e.g. for applications in the US 315MHz ISM band).
The transmitter's carrier frequency fc is determined
by the frequency of the reference crystal fref that is
used. The integrated PLL synthesizer ensures that
each RF value, ranging from 310 MHz to 450 MHz,
can be achieved by using a crystal with reference
frequency according to: fref = fc/N, where N = 32 is
the PLL feedback divider ratio.
Theory of Operation
General
As depicted in Fig.1, the TH71071 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 Po can be adjusted in six
steps from Po = –12 dBm to +2 dBm either by
changing the value of resistor R1 or by varying the
voltage VPS at pin PS/DATA. The open-collector
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 maximum available output power, the
differential output should be matched to a load of
approx. 1 kΩ.
Bandgap biasing ensures stable operation of the IC
at a power supply range of 2.2 V to 5.5 V.
ASK Modulation
The TH71071 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.
LO Source
Many applications require a stable RF source. For
this purpose, the TH71071 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.
ENTX
Mode
Description
0 TX disabled whole circuit in standby
1 TX enable TX active
Table 1: Modes of operation
3901071071
Rev. 004
Page 2 of 10
Data Sheet
Dec. 2001
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Block Diagram
TH71071
315/433MHz
ASK Transmitter / LO Source
Fig. 1: TH71071 block diagram with external components
3901071071
Rev. 004
Page 3 of 10
Data Sheet
Dec. 2001
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