TH71081 데이터 시트보기 (PDF) - Unspecified

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TH71081

868/915MHz ASK Transmitter / LO Source

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TH71081

868/915MHz ASK Transmitter / LO Source

Theory of Opera-

tion

ASK Modulation

The TH71081 can be ASK-modulated by

applying data at pin PS/DATA. The voltage

at this pin turns the power amplifier (PA)

on and off and therefore leads to an ASK

signal at the RF output. Both, simple on/off

keying (OOK) and true ASK are possible,

because the power of the PA can be set to

six different levels and one off state.

Frequency Modulation (FM)

For FM operation an external varactor is

required. It simply acts as a pulling ca-

pacitor connected in series to the crystal.

Then the analog modulation signal, applied

through a series resistor, directly modu-

lates the XOSC.

LO Source

Many applications require a stable RF

source. For this purpose, the TH71081 can

be used without modulation as an easy-to-

use, PLL-stabilized, continuous wave (CW)

generator.

General

The main parts of the TH71081 transmitter

are the fully integrated voltage-controlled

oscillator (VCO), the divide-by-32 divider

(div32), the phase-frequency detector

(PFD) and the charge pump. An external

loop filter at pin LF determines the dynamic

behaviour of the PLL and suppresses ref-

erence spurious signals.

The VCO’s output signal feeds the PA. RF

signal power Po can be adjusted, in six

steps from Po = –12 to +3 dBm, either by

changing the value of a resistor between

pin PS/DATA and ground or by varying the

voltage Vps at this pin. 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 im-

pedance 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. 0.5 to 1.5 kΩ .

Bandgap biasing ensures stable operation

of the IC at a power supply range of 2.0 to

5.5 V. The mode control logic allows the

transmitter to be set to standby mode or

active operation. The mode control pin

ENTX is internally connected to a pull-

down resistor. This guarantees that the

whole circuit is shut down if ENTX is left

open.

ENTX

Mode

Description

0 TX disabled whole circuit in stand by

1 TX enabled TX active

Rev. 1.0

Preliminary Datasheet

2

March 2000

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