• Supports clock and reset signals for the external µC.
• Supports different power down modes, one without any running XTAL oscillator.
• Wide supply range between 2.7 V to 5 V.
• Only one XTAL and very few external elements required.
• Wide operating temperature range from –40 C to +85 C.
• Low TX current, typical 7 mA.
General Description
The AS3901 is a low power FSK/ (ASK) transmitter intended for the European 433 MHz
and the US 315 MHz ISM band application. It uses a PLL stabilized oscillator which
avoids frequency pulling by approaching the antenna with objects as it occurs at SAW
resonator based transmitters.
FSK modulation is performed by an I/Q-based continuous phase FSK modulator with a
well defined frequency deviation of 16 kHz. The FSK modulator is operating completely
asynchronous to the TX data stream and therefore needs no data clock or other possible
by switching the driving amplifier and FSK modulator on and off by an applied transmit
data stream.
The µC clock frequency and the FSK frequency deviation can be kept almost constant
for both frequency bands by selecting the correct scaling factors by the 433/315 pin. As
external components the AS3901 needs only a reference XTAL and 5 capacitors.
STDBY
CLK
DATA
TX
GND
VDD
XTAL2
AS3901
8
NRES
GNDRF
ANT1
ANT2
VDDRF
433
XTAL1
TSSOP-14
Rev. 6, August 2000Page 2 of 18
Page 3
ISM 433/315 MHz FSK/ASK Transmitter – Data Sheet
AS3901
Applications
• Short range radio data transmission.
• Remote keyless entry systems.
• Security applications and alarm systems.
• Domestic and consumer remote control units.
• Remote metering.
• Low power telemetry.
This document contains information on products under development. Austria Mikro
Systeme International AG reserves the right to change or discontinue this product
without notice.
Rev. 6, August 2000Page 3 of 18
Page 4
ISM 433/315 MHz FSK/ASK Transmitter – Data Sheet
AS3901
XTAL2
Detector
AS3901
1Functional Description
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.
XTAL1
VDD
f =433.920 MHz
433
VDDRF
10
ANT2
11
ANT1
12
GNDRF
13
NRES
14
8
9
Driving
Amplifier.
Synthesizer
Loop-
Filter
Divider
Phase
SSB signal
generation
XTAL
Oscillator VCO
Clock
µC Interface +
Power up/down
7
VDD
6
GND
5
TX
4
DATA
3
CLK
2
STDBY
1
13.560 MHz
XTAL
Figure 1: Block diagram of the AS3901.
1.1RF Synthesizer
The RF synthesizer is a fully integrated single channel device with internal loop filter,
generating the 433 MHz or 315 MHz transmit carrier frequency fRF by a fix, 32 times,
multiplication of the reference XTAL frequency f
XTAL
.
1.2Microprocessor Clock
The microprocesor clock frequency f
by 3 or 4, dependent on the 433/315 MHz selection pin to keep the µC clock frequency
f
almost constant for European and US applications.
CLK
is generated by dividing the XTAL frequency f
CLK
1.3Modulation
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
XTAL or µC clock f
and no data synchronization of the FSK modulator is required.
CLK
XTAL
Rev. 6, August 2000Page 4 of 18
Page 5
ISM 433/315 MHz FSK/ASK Transmitter – Data Sheet
AS3901
1.4Driving 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 0.7 mA
.The maximal differential voltage swing is about 4 VPP. Therefore the
rms
output power ist a function of the connected load impedance. With a 2 kΩ 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.
1.5ASK 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.
1.6Power Management and Operation Modes
For normal operation the switching between different operation modes follows a Greycoded scheme to avoid unwanted switching between operation modes due to inaccurate
occurrence of edges of STDBY and TX/ASK.
ModeSTDBYTX/ASKFunction
Standby11All Off
Clock generator operation10XTAL oscillator on and CLOCK output
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.
Rev. 6, August 2000Page 5 of 18
Page 6
ISM 433/315 MHz FSK/ASK Transmitter – Data Sheet
AS3901
uC
I
O
O
I
I
I
I
O
O
O
TX/ASK
CLK
NRES
STDBY
standby
TX on
3 clocks
reset
init
PLLon
AS3901
STDBY
DATA
TX/ASK
STDBY
DATA
TX/ASK
RESETNRES
CLKCLK
10k
SW
Transmit
switch
Figure 2: Interconnection of the AS3901 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 5.
XTon
uC
transmitting
standby
Figure 3: µC interface timing for a transmission cycle.
Note:Activating the transmit switch results in a „weak L state“ at TX/ASK. It can be overridden by the
microcontroller so that the transmission cycle remains unaffected by the duration the switch is pressed. The STDBY and
TX/ASK inputs have internal pullup resistors of ~100kΩ
Rev. 6, August 2000Page 6 of 18
Page 7
ISM 433/315 MHz FSK/ASK Transmitter – Data Sheet
AS3901
1.7.1 Interface Description
Wake-up sequence:
TX/ASK=H, STDBY=H: Standby. All off low current state.
TX/ASK→L, STDBY=H; → XTAL oscillator starts up. NRES goes L, resetting (starting)
the µC for
NRES returns to H, µC initializes.
plus 3 clock cycles.
tXTON
After µC is initialized, it sets STDBY→L; PLL is turned on, after t
a stable RF carrier
PLLon
is generated.
TX/ASK→H, STDBY=L; →TX is turned on, t
later the RF signal is available and data
TXON
can be transmitted.
To switch the AS3901 „on“ a „push button“ with series resistance ~10-20 kΩ can be
used to make TX/ASK = „L“. The „push-button“ must be pushed long enough (typ. >
3ms) for the µC to reset and sustain the TX/ASK „L“ state.
Standby procedure (for sleep-mode ( IDD1 <1µA):
The µC outputs a „H“ to TX/ASK and STDBY. After minimal 3 CLK cycles the XTAL
oscillator will be switched off. The pull-up resistors at the AS3901 TX/ASK and STDBY
inputs will sustain the sleep mode.
Note: Multiple „push buttons“ for different functions can be used.
Rev. 6, August 2000Page 7 of 18
Page 8
ISM 433/315 MHz FSK/ASK Transmitter – Data Sheet
AS3901
2Electrical Characteristics
2.1 Absolute Maximum Ratings ( non operating)
SymbolParameterMinMaxUnitsNote
VDDPositive supply voltage-0.57V
GNDNegative supply voltage00V
V
IN
Voltage on input pins-0.5VDD+0.5V
ESDElectrostatic discharge1000V1)
T
STG
T
LEAD
Note:
1) HBM: R = 1.5 kΩ, C = 100 pF. The pins ANT1, ANT2, XTAL1 and XTAL2 have 500 V ESD protection.
2) 260°C for 10 s (reflow and wave soldering), 360 °C for 3 s (manual soldering).
10VDDRFPowerPositive supply (2.7 V-5.0 V)
11ANT2Analog open collector outputTo loop antenna
12ANT1Analog open collector outputTo loop antenna
13GNDRFPowerGround
14NRESETDig. OutputReset, „L“ state resets a microcontroller
Dig. Input, 100 kΩ pull up
Dig. Input, 100 kΩ pull up
Power down for all functions
Transmit data input (CMOS level)
Power off for TX (PLL and XTAL working)
ASK modulation
Selects division factors for constant µC
Clock frequency and deviation
Rev. 6, August 2000Page 13 of 18
Page 14
ISM 433/315 MHz FSK/ASK Transmitter – Data Sheet
100P
10P
10P
141312
11
8
4
321
C5
13.56MHZ
DATA
DATA
GND
VDD
XTAL2
XTAL1
433
VDDRF
ANT1
AS3901
4Application Schematic
VDD
C3
100N
STDBY
CLK
STDBY
CLK
U1
NRESET
NRES
GNDRF
VDD
A1
TX
C2
5
6
7
TX/ASK
AS3901
U2
ANT2
10
9
443_315
LOOP
ANTENNA
C4
C1
Figure 4:Basic application schematic of the AS3901.
3P
Figure 5:Pull Up characteristics for the TX/ASK pin.
Rev. 6, August 2000Page 14 of 18
Page 15
ISM 433/315 MHz FSK/ASK Transmitter – Data Sheet
AS3901
5Typical Measurements
Figure 6:Narrow band output spectrum of the AS3901 FSK modulated with pseudo
random data at 32 kbit/s.
Figure 7:Modulation bandwidth of the AS3901 in FSK operation at 32.6 kbit/s, measured
close to the EN 300-220-1 recommendation for wide-band equipment, clause 8.6.
Instead of 5 kHz video bandwidth (VBW) 10 kHz was used. The markers were set
up to the band edges. (433.050 MHz, 434.790 MHz) The recommendation says
that the spectrum should be observed at least 1MHz form the ISM band edges, but
it was measured with larger frequency span.
Rev. 6, August 2000Page 15 of 18
Page 16
ISM 433/315 MHz FSK/ASK Transmitter – Data Sheet
AS3901
Figure 8:Modulation bandwidth of the AS3901 in AKS operation at 9.2 kbit/s, measured
close to the EN 300-220-1 recommendatio for wide-band equipment, clause 8.6.
Instead of 5 kHz video bandwidth (VBW) 10 kHz was used. The markers were set
up to the band edges. (433.050 MHz, 434.790 MHz) The recommendation says
that the spectrum should be observed at least 1 MHz from the ISM band edges,
but it was measured with larger frequency span.
Figure 9:Spurious emissions of the AS3901 in FSK operation, measured close to the EN 300-220-
1Recommendation for wide-band equipment, clause 8.7, without modulation. (Only
difference: 100 kHz RBW was used instead of 120 kHz). From the measurement it can be
seen that the main critical spurious emission is generated by the 13.56 MHz clock frequency.
The level of CLK spurious is near –48 dBM so the suppression is 45 dB for this component.
Rev. 6, August 2000Page 16 of 18
Page 17
ISM 433/315 MHz FSK/ASK Transmitter – Data Sheet
AS3901
Figure 10:Typical out spectrum in ASK 9.2 kb/s PRN modulation.
Figure 11:Transmission power as function of time at ASK modulation with an 9.2 kbit/s 0101.. data
pattern.
Rev. 6, August 2000Page 17 of 18
Page 18
ISM 433/315 MHz FSK/ASK Transmitter – Data Sheet
AS3901
6Package Information
Figure 12:Physical dimensions of TSSOP-14.
Common Dimensions
Symbol
Minimal (mm)Nominal (mm)Maximal (mm)
A--1.20
A10.05-0.15
b0.19-0.30
D4.90-5.10
e0.65 BSC
E-6.40-
E14.30-4.50
L0.45-0.75
α
Copyright 2000, Austria Mikro Systeme International AG, Schloß Premstätten, 8141 Unterpremstätten, Austria.
Tel.: +43-(0)3136-500-0, Fax: +43-(0)3136-52501, E-Mail: info@amsint.com
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or
transmitted, in any form or by any means, without the prior permission in writing by the copyright holder.
To the best of its knowledge, Austria Mikro Systeme International asserts that the information contained
in this publication is accurate and correct.
0°-8°
Rev. 6, August 2000Page 18 of 18
Loading...
+ hidden pages
You need points to download manuals.
1 point = 1 manual.
You can buy points or you can get point for every manual you upload.