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

AS3901

Rev. 6, August 2000

Page 4 of 18

1

Functional Descriptio n

The AS3901 consists of a reference XTAL oscillator, a single channel RF- synthesizer,

an I/Q based asynchronous continuos phase FSK modulator, a driving amplifier and a

µC interface, including µC clock divider, and a power management circuitry.

AS3901

SSB signal

generation

ANT2

VDDRF

433

XTAL1

f =433.920 MHz

VDD

TX

4

STDBY

CLK

DATA

3

2

1

Driving

Amplifier.

Loop-

Filter

Synthesizer

XTAL

Oscillator

VCO

Clock

13.560 MHz

XTAL

GND

VDD

XTAL2

7

6

5

NRES

GNDRF

ANT1

14

13

12

11

10

9

8

Phase

Detector

Divider

32:1

µC Interface +

Power up/down

Figure 1:

Block diagram of the AS3901.

1.1 RF Synthesizer

The RF synthesizer is a fully integrated single channel device with internal loop filter,

1.2 Microprocessor Clock

by 3 or 4, dependent on the 433/315 MHz selection pin to keep the µC clock frequency

1.3 Modulation

The FSK modulator is an I/Q modulator based continuos phase FSK modulator. The

modulating NRZ data may be in the range of 0 up to 32 kbit/s. The FSK frequency

deviation

∆f is ≈16 kHz, independent of the data rate. It is also kept almost constant for

both transmit frequency bands by selecting proper frequency deviation multiplication

factors of the XTAL reference frequency by the 433/315 MHz selection pin.

The processing clock of the data source can be different from the AS3901 reference