MELEXIS TH7107 Datasheet

Features

! Fully integrated, PLL-stabilized VCO
! Flexible frequency range from 310 MHz to 450 MHz
! FSK through crystal pulling allows modulation from

DC to 20 kbit/s

! High FSK deviation possible for wideband data

transmission

! 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

TH7107

315/433MHz

FSK/FM/ASK Transmitter

! Adjustable output power range from

-12 dBm to +2 dBm

! Adjustable current consumption from

4.8 mA to 11.5 mA

! FSK deviation and center frequency

independently adjustable

! Differential output well-suited for loop

antenna

! External clock available for µC drive,

down to 1.9 V supply

! ”Clock only” mode
! Conforms to EN 300 220 and similar

standard

Ordering Information

Part No. Temperature Range Package

TH7107 -40 C° to 85 °C SOIC16

Application Examples Pin Description

! Keyless car and central locking
! Low-power telemetry
! Alarm and security systems
! General digital data transmission
! General analog audio signal transmission

LF1

SUB

DAT A

RO2

RO1

ENTX

ENCK

CKOUT

1

2

3

4

TH7107

5

6

7

8

16

15

14

13

12

11

10

9

LF2
VCC
VEE
OUT1
OUT2
VEE

VCC
PS

3901007107 Page 1 of 14 Data Sheet
Rev. 005 Dec. 2001

General Description

TH7107

315/433MHz

FSK/FM/ASK Transmitter

The TH7107 FSK/ASK/FM 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).

Theory of Operation

General

As depicted in Fig.1, the TH7107 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 behavior 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

= –12 dBm to +2 dBm either by

o

changing the value of resistor R
voltage V

at pin PS. The open-collector differential

PS

output (OUT1, OUT2) can be used to either directly
drive a loop antenna or to be converted to a single­ended impedance by means of a balanced-to­unbalanced (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.

FSK Modulation

A Colpitts crystal oscillator (XOSC) is used as the
reference oscillator of a phase-locked loop (PLL)
synthesizer. FSK modulation is achieved by pulling
the crystal (XTAL) through the data. So a CMOS­compatible 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

); while at DATA = HIGH CX2 is

min

deactivated and the XOSC is set to its high
frequency, leading to f
An external reference signal can be directly AC­coupled to pin RO1. Then the TH7107 is used
without an XTAL. The reference signal has to
contain the FSK (or FM) and sets the carrier
frequency.

can be adjusted in six

o

or by varying the

PS

.

max

The transmitter's carrier frequency f
by the frequency of the reference crystal f

is determined

c

that is

ref

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: f

= fc/N, where N = 32 is

ref

the PLL feedback divider ratio.

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.

ASK Modulation

The TH7107 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.

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 pulled­down 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
required for any specific application. Clock
frequency is 1/4 of the reference crystal frequency.

ENCK ENTX Mode Description

0 0 all OFF whole circuit in standby

0 1 TX only TX functionality only, no

clock available

10clock

only

11all ON

TX in standby and clock
available

TX functional and clock
available

Table 1: Modes of operation

3901007107 Page 2 of 14 Data Sheet
Rev. 005 Dec. 2001

Block Diagram

RPS

VEE

14

OUT1

13

VCC

OUT2

12

VEE

11

ENCK

7

TH7107

315/433MHz

FSK/FM/ASK Transmitter

ENTX

6

PA

div32

XOSC

VCC 10 VCC PS15 9

div 4

8

RO1

CKOUT

VCO

PFD

mode

control

2LF2 SUB

16

pump

charge

1

DATA LF1

3

5

XTAL

4

RO2

CX2

CX1

CF1

CF2

RF1

Fig. 1:TH7107 block diagram with external components

3901007107 Page 3 of 14 Data Sheet
Rev. 005 Dec. 2001

TH7107

315/433MHz

FSK/FM/ASK Transmitter

Pin Definition and Descripti on

Pin No. Name I/O Type Functional Schematic Description

1 LF1 output

charge pump output,
connection to loop filter

LF1

1

200

Ω

2 SUB ground negative power supply,

substrate connection

3 DATA input

FSK data input,
CMOS-compatible

DATA

3

1.8k

4 RO2 analog I/O

XOSC FSK pulling pin,
MOS switch

RO2

4

5 RO1 analog I/O

RO1

37k

XOSC connection to XTAL,
Colpitts type crystal
oscillator

6 ENTX input

7 ENCK input

ENTX

6

ENCK

7

5

28p

28p

mode control input, CMOS­compatible with internal pull-

1.1k

down

mode control input, CMOS­compatible with internal pull-

1.1k

down

3901007107 Page 4 of 14 Data Sheet
Rev. 005 Dec. 2001

TH7107

315/433MHz

FSK/FM/ASK Transmitter

Pin No. Name I/O Type Functional Schematic Description

8 CKOUT output

clock output,
CMOS-compatible

CKOUT

8

200

Ω

9 PS analog I/O

power-select and ASK input,
high-impedance comparator

PS

20µA

200

Ω

9

logic

10 VCC supply positive power supply

11 VEE ground negative power supply

12 OUT2 output differential power amplifier

VCC

VCC

output, open collector

OUT2

OUT1

13 OUT1 output

12

13

differential power amplifier
output, open collector

VEE

VEE

VEE

14 VEE ground negative power supply

15 VCC supply positive power supply

16 LF2 input

VCO tuning input,
connection from loop filter

LF2

16

200

Ω

5p

3901007107 Page 5 of 14 Data Sheet
Rev. 005 Dec. 2001