ISM 433 MHz ASK Transmitter – Preliminary Data Sheet

AS3902

Rev. A7, December 2000

Page 4 of 14

1.3 Modulation

ASK modulation with a data rate from 0 up to 32 kbit/s (for continuous 101010… modulation

pattern) is done by turning the synthesizer and the driving amplifier on and off, whereas a TXD

= “H“means a turned on state.

When TXD = “H“, at first the synthesizer is turned on. The following turning on of the driving

synthesizer to lock and settle its frequency prior to transmitting. When TXD becomes “L“, both,

synthesizer and driving amplifier are turned off to save power. In this case the synthesizer turn

off is delayed for 21 µs.

1.4 Driving Amplifier

The driving amplifier has a differential open collector output optimized for driving of small,

symmetrical high-impedance loop antennas. The amplifier drives a nominal RF current of

put power is a function of the connected load impedance. With a 2 k

Ω differential load a nomi-

nal output power (to the antenna) of

≈1 mW is obtained. Please note that the finally radiated

power (from antenna) is lower and strongly dependent on the efficiency (function of the size)

of the antenna to be used.

1.5 µC Interface and Power Management

The AS3902 contains a direct interface to a microcontroller (

µC). The µC interface of the

AS3902 consists of the following three pins:

“Transmit data input“(TXD).

“Active “L“µC reset output/transmitter power down input“(NRES/PD).

“µC clock output/active “L“wake-up input“(CLK/NWUP).

These lines support the µC with the required reset and clock signals and control the AS3902

internal power on/off circuit which wakes up and shuts down the whole transmitter consisting

of the AS3902 and the µC.

Figure 2 shows a typical interconnection of the AS3902 with a typical µC. Figure 3 presents a

related timing for power up and down of the transmitter.

P1 SERIAL DATA OUT

P2 END TRANSMIT

NRESET

CLOCK

CLK/NWUP

TXD

NRES/PD

10k

uC

10k

Transmit

switch

SW

I

O

O

I/O

I/O

I

I

Figure 2:

Interconnection of the AS3902 with a typical µC.

Note:

At room temperature, resistor values of

≈10 kΩ are suggested for the µC interface.

For other temperatures to be calculated from figure 6.

AS3902