EVB7108B-868-FSK-A - Melexis Technologies NV

EVB7108

868/915MHz Transmitter

Evaluation Boar d Descr i ption

390120710801 1 of 8 EVB Description

Rev. 007 Aug/02

General Description

The TH7108 antenna board is designed to

optimally match the differential power amplifier

output to a loop antenna. The TH7108 can be

populated either for FSK, ASK or FM

transm ission. The default population is for FSK or

ASK transmission. Adding a varactor diode can

easily be done in order to modify the circuit for

analog FM. The evaluation board contains a

differential-drive loop antenna printed on the PCB

(Printed Circuit Board). The size of the loop

antenna is matched to the resonant frequency.

Board layout data in Gerber format is available on reques t.

Features

! Full y integrate d, PLL- s ta bi lize d VC O

! Flexible frequency range from

850 MHz to 930 MHz

! FSK through crystal pulling allows modulation

from DC to 20 kbit/s

! High 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

! Adjustable equivalent radiated power (ERP)

range from -20 dBm to -6 dBm

! Adjustable current consumption from

6.2 mA to 12.5 mA

! Frequency deviation and center frequency

independe ntly adjustable

! Differential output well-suited for loop antenna

! External clock available for µC drive,

down to 1.9 V suppl y

! ”Clock only” mode

! Conforms to EN 300 220 standard

Ordering Informati on

Part No.

EVB7108-868-FSK EVB7108-915-FSK

EVB7108-868-ASK EVB7108-915-ASK

Applications

! Keyless car and central locking

! Low-power telemetry

! Alarm and security systems

! General digital data transmission

! General analog audio signal transmission

EVB7108

868/915MHz Transmitter

Evaluation Boar d Descr i ption

390120710801 2 of 8 EVB Description

Rev. 007 Aug/02

Theory of Oper ation

General

As depicted in Fig.1, the TH7108 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 = –15 dBm to +1 dBm either by

changing the value of resistor RPS or by varying the

voltage VPS at pin PS. The open-collector differential

output (OUT 1, OUT2) can be used to either directl y

drive a loop antenna or to be converted t o 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 operatio n 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 CMOS-

compatible data stream applied at input DATA

digitally modulates the XOSC. Two external pulling

capacitors CX1 and C X2 allow the F SK deviat ion and

center frequency to be adjusted independently. At

DATA = LOW CX2 is connected in parallel to CX1

leadin g to the low-f requency c omponent of the F SK

spectrum (fmin); while at DATA = HIGH CX2 is

deactivated and the XOSC is set to its high

frequency, leading to fmax.

An external reference signal can be directly AC-

coupled to pin RO1. Then the TH7108 is used

without an XTAL. The reference signal has to

contain the FSK (or FM) and sets the carrier

frequency.

Frequency Modulation (FM)

For FM operati on an external varactor is requir ed. 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 TH7108 can be ASK-modulated by applying

data direc tly at pin PS. This turns t he PA on and of f

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 pulled-

down 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 1/8 of the reference crystal frequency.

The clock output is slew-rate limited in order to keep

spurious signal emission as low as possible. The

voltage s wing at C KOUT depends on the ca pacitive

loading at this pin. It is approx. 2 Vpp at Cload = 5 pF.

ENCK ENTX Mode Description

0 0 all OFF whole circuit in standby

0 1 TX only TX functionality only, no

clock available

10clock

only TX in standby and clock

available

1 1 all ON TX functional and clock

available

Table 1: Modes of operation

For more detailed information, please refer to the latest TH7108 data sheet revision.

EVB7108

868/915MHz Transmitter

Evaluation Boar d Descr i ption

390120710801 3 of 8 EVB Description

Rev. 007 Aug/02

Block Diagram

Fig. 1: TH7108 block diagram with external components

DATA LF1116 2LF2 SUB

CKOUT

VEE

OUT1

OUT2

PA VCC

ENTX

mode

control

VCO VEE

ENCK

PFD

XOSC

div32

div 8

charge

pump

RF1

RPS

CF2

CF1

RO2

RO1

XTAL

CX1

CX2

VCC 10 VCC PS15 9

EVB7108

868/915MHz Transmitter

Evaluation Boar d Descr i ption

390120710801 4 of 8 EVB Description

Rev. 007 Aug/02

Circuit Diagram

C1 C2

LF2

VCC

VEE

OUT1

OUT2

ENTX

SUB

LF1

DATA

RO1

RO2

ENCK

CKOUT

C3 L2

XTAL

CX2

CX1

RF1

CX3

CF1

CF2

C4 RPS

RF2

ENTX

CKOUT

GND

ENCK

GND

VCC

121212 3

VCC

GND

FSK

GND

FM/ASK

GND

EVB7108

868/915MHz Transmitter

Evaluation Boar d Descr i ption

390120710801 5 of 8 EVB Description

Rev. 007 Aug/02

PCB Top View

Board size is 34mm x 44mm

Board Connection

VCC Power supply (2.2 V to 5.5 V) ENCK Mode control pin (see table 1)

FSK Input for FSK data (CMOS) ENTX Mode control pin (see table 1)

FM/ASK Input for FM signal (analog) or ASK data (CMOS) GND Several ground pins

CKOUT Clock output (3.4 MHz)

VCC

ENCK

CKOUT

ENTX

FM/ASK

VCC

GND

FSK

GND

XTAL

C4 C3

CF1

CF2

RPS

RF1 RF2

R1 CX1

Cx3

CX2

TH7108

16 9

11 11

EVB7108

868/915MHz Transmitter

Evaluation Boar d Descr i ption

390120710801 6 of 8 EVB Description

Rev. 007 Aug/02

Board Component Values

Part Size Value

868.3 MHz Value

915 MHz Tolerance Description

CF1 0805 5.6 nF 4.7 nF ±10% loop filter capacitor

CF2 0805 27 pF 27 pF ±10% loop filter capacitor

CX1_FSK 0603 56 pF 56 pF ±5% XOSC capacitor for FSK (∆f = ±30 k Hz)

CX1_ASK 0603 18 pF 18 pF ±5% XOSC capacitor for ASK, trimmed to fC

CX2 0603 1 nF 1 nF ±5% XOSC capacitor, only needed for FSK

CX3 0603 1 nF 1 nF ±10% XOSC capacitor, only needed for FM

C1 1206 2.2 pF 2.2 pF ±2% antenna resonance capacitor

C2 0805 1.2 pF 1 pF ±2% antenna resonance capacitor

C3 0603 330 pF 330 pF ±10% blocking capacitor

C4 0603 330 pF 330 pF ±10% blocking capacitor

C5 1206 220 nF 220 nF ±20% blocking capacitor

L1 0603 150 nH 150 nH ±10% biasing induct or

L2 0603 150 nH 150 nH ±10% biasing induct or

RF1 0805 1.6 kΩ1.6 kΩ±10% loop filter resistor

RF2 0805 2.0 kΩ2.0 kΩ±10% loop filter resistor

RPS 0805 47 kΩ47 kΩ±10% power-select resistor

R1 0805 470 kΩ470 kΩ±10% optional pull-up r es ist or, typically not needed

R2 0805 30 kΩ30 kΩ±10% varactor bias resistor, only needed for FM

R3 0805 0 Ω0 Ω±10% ASK jumper, only needed for ASK

V1 SOD323 BB535 varactor diode, only needed for FM

XTAL HC49/S 27.1344 MHz

fundamental

wave

28.5938 MHz

fundamental

wave

±30ppm

calibration

±30ppm

temp.

crystal, Cload = 12 pF to 15 pF, C0, max = 7 pF,

Rm, max = 40 Ω

PCB

loop

antenna

long side

length 18 mm 18 mm on FR4 PCB material

side length including length of C1 and C2

PCB

loop

antenna

small sid e

length 9 mm 9 mm on FR4 PCB material

PCB

loop

antenna

Line width 2 mm 2 mm on FR4 PCB material

The listed component va lues are default values. Al l va lues might be c ha nge d to fit to any specif ic ap pl ic ation.

As for example FSK deviation can be set by varying CX1 and CX2, output power at FSK/FM transmission

can be changed through RPS or through RPS and R3 at ASK transmission, respectively.

Pads for C1 are for population of a fixed-value capacitor with size 1206 or a to use trimming capacitor either.

EVB7108

868/915MHz Transmitter

Evaluation Boar d Descr i ption

390120710801 7 of 8 EVB Description

Rev. 007 Aug/02

Package Infor mation

Fig. 2: QSOP16

all Dimension in mm, coplanarity < 0.1mm

DE1 E A A1 e b L α

αα

min 4.80 3.81 5.79 1.35 0.10 0.635 0.20 0.40 0°

max 4.98 3.99 6.20 1.75 0.25 0.30 1.27 8°

all Dimension in inch, coplanarity < 0.004”

min 0.189 0.150 0.228 0.0532 0.0040 0.025 0.008 0.016 0°

max 0.196 0.157 0.244 0.0688 0.0098 0.012 0.050 8°

123

E1 E

A1 A

EVB7108

868/915MHz Transmitter

Evaluation Boar d Descr i ption

390120710801 8 of 8 EVB Description

Rev. 007 Aug/02

Disclaimer

Devices sold by Melexis are covered by the warranty and patent indemnification provisions appearing in its

Term of Sale. Melexis makes no warranty, express, statutory, implied, or by description regarding the

information set forth herein or regarding the freedom of the described devices from patent infringement.

Melexis reserves the right to change specifications and prices at any time and without notice. Therefore, prior

to designing this product into a system, it is necessary to check with Melexis for current information. This

product is intended for use in normal commercial applications. Applications requiring extended temperature

range, unusual environmental requirements, or high reliability applications, such as military, medical life-

support or life-sustaining equipment are specifically not recommended without additional processing by

Melexis for each application.

The information furnished by Melexis is believed to be correct and accurate. However, Melexis shall not be

liable to recipient or any third party for any damages, including but not limited to personal injury, property

damage, loss of profits, loss of use, interrupt of business or indirect, special incidental or consequential

damages , of an y kind, in conn ectio n with or aris ing o ut of th e fur nishing, per formance or use of the tech nica l

data here in. No o bl iga tio n or li abi l it y to rec i pient or any third party shall aris e or f lo w ou t of Mel ex is’ renderin g

of technical or other services.

For the latest version of t his docum ent. Go to our website at

www.melexis.com

Or for additional i nformation contact Melexis Direct:

Europe and Japan: All other locations:

Phone: +32 1367 0495 Phone: +1 603 223 2362

E-mail: sales_europe@melexis.com E-mail: sales_usa@melexis.com

QS9000, VDA 6.1 an d ISO 140 01 Cer tif ied