ISM 433/315 MHz FSK/ASK Transmitter – Data Sheet

AS3901

Rev. 6, August 2000

Page 5 of 18

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

output power ist a function of the connected load impedance. With a 2 k

Ω differential

load a nominal peak 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 ASK Modulation

ASK modulation with a date rate upt to 20 kbits/s can be achieved by turning the driving

amplifier and the FSK modulator by the TX/ASK pin on and off, where a TX/ASK = „H“

means a turned on state.

1.6 Power Management and Operation Modes

For normal operation the switching between different operation modes follows a Grey-

coded scheme to avoid unwanted switching between operation modes due to inaccurate

occurrence of edges of STDBY and TX/ASK.

Mode

STDBY

TX/ASK

Function

Standby

1

1

All Off

Clock generator operation

1

0

XTAL oscillator on and CLOCK output

active.

Transmit operation

0

1

XTAL oscillator, PLL, FSK modulator

running, (FSK operation or „H“transmitted

at ASK).

Turned off power

0

0

XTAL oscillator and PLL running, output

amplifier and FSK modulator off, („L“

transmitted at ASK).

1.7 µC Interface and Timing

The AS3901 contains a direct interface to a microcontroller (µC). The µC interface of the

AS3901 consists of three input and two outputs pins:

„Standby input“(STDBY).

„Transmit / ASK input“(TX/ASK).

„µC reset output (Active „L“)“(NRES).

„µC clock output“(CLK).

„FSK data input“(DATA).

These lines support the µC with the required reset, clock and data signals. Lines 1 to 4

control the AS3901 internal power on/off circuit which wakes up and shuts down the

whole transmitter consisting of the AS3901 and the µC.

Figure 2 shows a typical interconnection of the AS3901 with a typical µC. Figure 3

presents a related timing for power up and down of the transmitter.