TH7108

868/915MHz

FSK/FM/ASK Transmitter

3901007108

Page 3 of 14

Data Sheet

Rev. 008

May/03

1

Theory of Operation

1.1

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 behavior of the PLL and suppresses reference spurious signals. The

PS. 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 about 1 k

Ω.

Bandgap biasing ensures stable operation of the IC at a power supply range of 2.2 V to 5.5 V.

1.2

Block Diagram

Fig. 1: Block diagram with external components

LF1

1

16

2

LF2

SUB

PA

mode

control

VCO

PFD

div32

charge

pump

RF1

RPS

CF2

CF1

VCC

PS

15

9

DATA

CKOUT

3

4

5

8

XOSC

div 8

RO2

RO1

XTAL

CX1

CX2

VCC 10

VEE

14

OUT1

OUT2

VCC

13

12

11

ENTX

VEE

ENCK

7

6

antenna

or

balun