TH72005

315MHz

FSK/ASK Transmitter

3901072005

Page 3 of 20

Data Sheet

Rev. 011

Jul/12

1 Theory of Operation

1.1

General

As depicted in Fig.1, the TH72005 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 (CP). An

internal loop filter determines the dynamic behavior of the PLL and suppresses reference spurious signals. A

Colpitts crystal oscillator (XOSC) is used as the reference oscillator of a phase-locked loop (PLL)

loop antenna or to be matched to a 50Ohm load. Bandgap biasing ensures stable operation of the IC at a

power supply range of 1.95 V to 5.5 V.

1.2

Block Diagram

Fig. 1: Block diagram with external components

2 Functional Description

2.1

Crystal Oscillator

A Colpitts crystal oscillator with integrated functional capacitors is used as the reference oscillator for the PLL

synthesizer. The equivalent input capacitance CRO offered by the crystal oscillator input pin ROI is about

18pF. The crystal oscillator is provided with an amplitude control loop in order to have a very stable

frequency over the specified supply voltage and temperature range in combination with a short start-up time.

CX1

FSKDTA

antenna

matching

network

XOSC

PA

XBUF

VCO

PLL

CP

PFD

32

OUT

PSEL

RPS

FSKSW

ROI

XTAL

CX2

VEE

7

VEE

9

2

8

6

4

3

1

ASKDTA

low

voltage

detector

10

VCC

mode

control

ENTX

5