AS3901
ISM 433/315 MHz
FSK/ASK Transmitter
Data Sheet
Rev. 06, August 2000
ISM 433/315 MHz FSK/ASK Transmitter Data Sheet
AS3901
Rev. 6, August 2000
Page 2 of 18
Key Features
Supports the European 433 MHz ISM band.
No frequency pulling by (antenna) load variation due to PLL synthesizer.
Designed to be conform to EN 300 220-1 requirements.
Supports FSK (data rates 0... 32 kb/s) or ASK modulation (data rates 0... 20kb/s)
No data synchronization for FSK or ASK needed.
Supports clock and reset signals for the external C.
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 C 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.
TSSOP-14
STDBY
CLK
DATA
TX
NRES
ANT1
ANT2
GNDRF
AS3901
GND
VDD
1
2
3
4
5
6
7
XTAL2
433
XTAL1
VDDRF
8
9
10
11
12
13
14
ISM 433/315 MHz FSK/ASK Transmitter Data Sheet
AS3901
Rev. 6, August 2000
Page 3 of 18
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.
ISM 433/315 MHz FSK/ASK Transmitter Data Sheet
AS3901
Rev. 6, August 2000
Page 4 of 18
1
F u n c t i o n a l D e s c r i p t i o 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
C interface, including C 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
C 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,
generating the 433 MHz or 315 MHz transmit carrier frequency f
RF
by a fix, 32 times,
multiplication of the reference XTAL frequency f
XTAL
.
1.2 Microprocessor Clock
The microprocesor clock frequency f
CLK
is generated by dividing the XTAL frequency f
XTAL
by 3 or 4, dependent on the 433/315 MHz selection pin to keep the C clock frequency
f
CLK
almost constant for European and US applications.
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
XTAL or C clock f
CLK
and no data synchronization of the FSK modulator is required.
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
current of 0.7 mA
rms
.The maximal differential voltage swing is about 4 V
PP
. Therefore the
output power ist a function of the connected load impedance. With a 2 k
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 C Interface and Timing
The AS3901 contains a direct interface to a microcontroller (C). The C interface of the
AS3901 consists of three input and two outputs pins:
,,Standby input" (STDBY).
,,Transmit / ASK input" (TX/ASK).
,,C reset output (Active ,,L")" (NRES).
,,C clock output" (CLK).
,,FSK data input" (DATA).
These lines support the C 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 C.
Figure 2 shows a typical interconnection of the AS3901 with a typical C. Figure 3
presents a related timing for power up and down of the transmitter.
ISM 433/315 MHz FSK/ASK Transmitter Data Sheet
AS3901
Rev. 6, August 2000
Page 6 of 18
AS3901
STDBY
DATA
TX/ASK
RESET
NRES
TX/ASK
uC
10k
Transmit
switch
SW
STDBY
I
O
O
I
DATA
I
CLK
CLK
I
I
O
O
O
Figure 2:
Interconnection of the AS3901 with a typical C.
Note:
At room temperature, resistor values of
10 k
are suggested for the C interface.
For other temperatures to be calculated from figure 5.
TX/ASK
CLK
NRES
STDBY
standby
XTon
TX on
transmitting
3 clocks
standby
reset
uC
init PLLon
Figure 3:
C 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 ~100k
ISM 433/315 MHz FSK/ASK Transmitter Data Sheet
AS3901
Rev. 6, August 2000
Page 7 of 18
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 C for
tXTON
plus 3 clock cycles.
NRES returns to H, C initializes.
After C is initialized, it sets STDBY
L; PLL is turned on, after t
PLLon
a stable RF carrier
is generated.
TX/ASK
H, STDBY=L;
TX is turned on, t
TXON
later the RF signal is available and data
can be transmitted.
To switch the AS3901 ,,on" a ,,push button" with series resistance ~10-20 k
can be
used to make TX/ASK = ,,L". The ,,push-button" must be pushed long enough (typ. >
3ms) for the C to reset and sustain the TX/ASK ,,L" state.
Standby procedure (for sleep-mode ( IDD1 <1A):
The C 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.
ISM 433/315 MHz FSK/ASK Transmitter Data Sheet
AS3901
Rev. 6, August 2000
Page 8 of 18
2
E l e c t r i c a l C h a r a c t e r i s t i c s
2.1 Absolute Maximum Ratings ( non operating)
Symbol
Parameter
Min
Max
Units
Note
VDD
Positive supply voltage
-0.5
7
V
GND
Negative supply voltage
0
0
V
V
IN
Voltage on input pins
-0.5
VDD+0.5
V
ESD
Electrostatic discharge
1000
V
1)
T
STG
Storage temperature
-55
125
C
T
LEAD
Lead temperature
260
C
2)
Note:
1)
HBM: R = 1.5 k
, C = 100 pF. The pins ANT1, ANT2, XTAL1 and XTAL2 have 500 V ESD protection.
2)
260C for 10 s (reflow and wave soldering), 360 C for 3 s (manual soldering).
2.2 Operating Conditions
Symbol
Parameter
Min
Typ
Max
Unit
Note
VDD
Positive supply voltage
2.7
3.0
5.0
V
GND
Negative supply voltage
0
0
0
V
IDD1
Supply current,
STDBY = "H", TX/ASK = "H"
1
A
1)
IDD2
Supply current,
STDBY = "H", TX/ASK = "L"
350
850
A
2)
IDD3
Supply current,
STDBY = "L", TX/ASK = "H"
7
9
mA
3)
IDD4
Supply current,
STDBY = "L", TX/ASK = "L"
3.5
4.5
mA
4)
T
AMB
Ambient temperature range
-40
+85
C
Note:
1)
Standby:
T
AMB
= 23 C, Synthesizer and driving amplifier are turned off.
2)
Clock generator operation:
T
AMB
= 23 C XTAL oscillator and C clock divider on. RF driving amplifier and PLL off, no
external load connected to CLK pin.
3)
Transmit operation:
T
AMB
= 23 C, Synthesizer and driving amplifier are turned on.
4)
Turned off TX power:
T
AMB
= 23 C, XTAL oscillator and C clock divider and PLL on RF driving amplifier off.
ISM 433/315 MHz FSK/ASK Transmitter Data Sheet
AS3901
Rev. 6, August 2000
Page 9 of 18
2.3 Transmit Operation
T
AMB
= 23 C, VDD = 3.0 V, unless specified otherwise.
Symbol
Parameter
Conditions
Min
Typ
Max
Units
Note
f
RF, EU
Transmit frequency (Europe) f
XTAL
= 13.560 MHz
433.920
MHz
1)
f
RF, US
Transmit frequency (US)
f
XTAL
= 9.84375 MHz
315.000
MHz
1)
f
offset
Frequency tolerance
After t
TXON
, no XTAL
tolerance.
2
kHz
f
CLK, EU
C clock frequency (Europe) f
XTAL
= 13.560 MHz
3.390
MHz
f
CLK, US
C clock frequency (US)
f
XTAL
= 9.84375 MHz
3.28125
MHz
t
TXon
Transmitter turn on time
FSK modulator and
driver amplifier
20
s
t
PLLon
PLL turn on time
t.b.d.
ms
T
XTon
XTAL oscillator turn on time
5
ms
Note:
1)
XTAL tolerances will slightly change the typical transmit frequency.
2.3.1 ASK Operation
T
AMB
= 23 C, VDD = 3.0 V, unless specified otherwise.
Symbol
Parameter
Conditions
Min
Typ
Max
Units
Note
P
OUT
,H
Available peak output
power
In 2 k
, STDBY = "L",
TX/ASK = "H"
-1.5
0
1.5
dB
m
1) 3)
P
OUT
,L
Leakage peak output
power
In 2 k
, STDBY = "L",
TX/ASK = "L"
-50
dB
m
P
OUT
3rd
Radiated third harmonic
output power
Antenna attenuation>
20 dB
-39
dB
m
2)
P
SP
Spurious power
In distance of f
CLK
or
f
XTAL
from carrier. No
antenna selectivity
assumed.
-45
-25
dB
C
2) 3)
R
ASK
ASK data rate range
For a RF packet duty
cycle
25 %.
0
20
Kb/s
Note:
1)
Output power depends on load impedance, differential output current is typical 0.7 mA
rms
. Maximum differential voltage swing
is typical 4 V
PP
.
2)
Measurement bandwidth (close to EN 300 220-1) see also figure 10.
3)
Actual E.R.P. depends on antenna efficiency
ISM 433/315 MHz FSK/ASK Transmitter Data Sheet
AS3901
Rev. 6, August 2000
Page 10 of 18
2.3.2 FSK Operation
T
AMB
= 23 C, VDD = 3.0 V, unless specified otherwise.
Symbol
Parameter
Conditions
Min
Typ
Max
Units
Note
P
OUT
,FSK Available peak output
power
In 2 k
, STDBY = "L",
TX/ASK = "H"
-1.5
0
1.5
dB
m
1) 3)
P
OUT
3rd
Radiated third harmonic
output power
Antenna and band pass
filter attenuation> 20 dB
-36
dB
m
2)
P
SP
Spurious power
In distance of f
CLK
or
f
XTAL
from carrier. No
antenna selectivity
assumed.
-45
-25
dB
C
2) 3)
R
FSK
FSK data rate range
0
32
kb/s
4)
f
FSK frequency deviation
16
kHz
Note:
1)
Output power depends on load impedance, differential output current is typical 0.7 mA
ms
. Maximum differential voltage
swing is typical 4 V
PP
.
2)
Measurement bandwidth (close to EN 300 220-1) see also figure 10.
3)
Actual E.R.P. depends on antenna efficiency
4)
Guaranteed by design
ISM 433/315 MHz FSK/ASK Transmitter Data Sheet
AS3901
Rev. 6, August 2000
Page 11 of 18
2.4 Digital Pin Characteristics
T
AMB
= 23 C, VDD = 3.0 V, unless specified otherwise. GND is the 0 V reference.
Symbol Parameter
Conditions
Min
Typ
Max
Units Note
CLK (C clock output)
VOH
High level output voltage IOH = -1 mA
VDD-0.7
-
VDD
V
VOL
Low level output voltage IOL = 1 mA
GND
-
1.2
V
tr
Rise time
CLoad = 10 pF
20
ns
td
Fall time
CLoad = 10 pF
20
ns
jcc
Cycle to cycle jitter
+/-5
%
1)
NRES (Inverted reset output)
VOH
High level output voltage IOH = -1 mA
VDD-0.3
-
VDD
V
VOL
Low level output voltage IOL = 1 mA
GND
-
0.2
V
tr
Rise time
CLoad = 10 pF
20
ns
td
Fall time
CLoad = 10 pF
20
ns
TX/ASK (Driving amplifier and FSK modulator on/off (ASK) input)
VIH
High level input voltage
VDD-0.5
-
VDD
V
VIL
Low level input voltage
GND
-
0.3
V
IIH
High level input current
VIH = VDD
1
IIL
Low level input current
VIL = 0 V.
internal pull-up
-40
A
DATA (FSK data input)
VIH
High level input voltage
VDD-0.5
-
VDD
V
VIL
Low level input voltage
GND
-
0.3
V
IIH
High level input current
VIH = VDD
1
A
IIL
Low level input current
VIL = 0 V
-1
A
ISM 433/315 MHz FSK/ASK Transmitter Data Sheet
AS3901
Rev. 6, August 2000
Page 12 of 18
433/315 (Band selection (division ratio))
VIH
High level input voltage
VDD-0.5
-
VDD
V
VIL
Low level input voltage
GND
-
0.3
V
IIH
High level input current
VIH = VDD
1
A
IIL
Low level input current
VIL = 0 V.
-1
A
STANDBY (Standby input)
VIH
High level input voltage
VDD-0.5
VDD
V
VIL
Low level input voltage
GND
-
0.3
V
IIH
High level input current
VIH = VDD
1
A
1IIL
Low level input current
VIL = 0 V.
internal pull-up
-40
A
Notes
1)
Guaranteed by design
ISM 433/315 MHz FSK/ASK Transmitter Data Sheet
AS3901
Rev. 6, August 2000
Page 13 of 18
3
P i n - o u t I n f o r m a t i o n
Pin # Pin Name
Input / Output
Description
1
STDBY
Dig. Input, 100 k
pull up
Power down for all functions
2
CLK
Dig. Output
Clock output (CMOS level)
3
DATA
Dig. Input
Transmit data input (CMOS level)
4
TX/ASK
on/off ASK
Dig. Input, 100 k
pull up
Power off for TX (PLL and XTAL working)
ASK modulation
5
GND
Power
Ground
6
VDD
Power
Positive supply (2.7 V-5.0 V)
7
XTAL2
Analog
XTAL pin2
8
XTAL1
Analog
XTAL pin1
9
433/315
Dig. Input
Selects division factors for constant
C
Clock frequency and deviation
10
VDDRF
Power
Positive supply (2.7 V-5.0 V)
11
ANT2
Analog open collector output
To loop antenna
12
ANT1
Analog open collector output
To loop antenna
13
GNDRF
Power
Ground
14
NRESET
Dig. Output
Reset, ,,L" state resets a microcontroller
ISM 433/315 MHz FSK/ASK Transmitter Data Sheet
AS3901
Rev. 6, August 2000
Page 14 of 18
4
A p p l i c a t i o n S c h e m a t i c
3P
100P
10P
10P
100N
C4
C3
C2
U1
14
13
12
11
10
9
8
7
6
5
4
3
2
1
C5
LOOP
ANTENNA
VDD
NRES
443_315
C1
13.56MHZ
A1
STDBY
CLK
DATA
TX
STDBY
CLK
DATA
TX/ASK
GND
VDD
XTAL2
XTAL1
433
VDDRF
ANT2
ANT1
GNDRF
NRESET
AS3901
U2
VDD
Figure 4:
Basic application schematic of the AS3901.
Figure 5:
Pull Up characteristics for the TX/ASK pin.
ISM 433/315 MHz FSK/ASK Transmitter Data Sheet
AS3901
Rev. 6, August 2000
Page 15 of 18
5
T y p i c a l M e a s u r e m e n t s
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.
ISM 433/315 MHz FSK/ASK Transmitter Data Sheet
AS3901
Rev. 6, August 2000
Page 16 of 18
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.
ISM 433/315 MHz FSK/ASK Transmitter Data Sheet
AS3901
Rev. 6, August 2000
Page 17 of 18
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.
ISM 433/315 MHz FSK/ASK Transmitter Data Sheet
AS3901
Rev. 6, August 2000
Page 18 of 18
6
P a c k a g e I n f o r m a t i o n
Figure 12:
Physical dimensions of TSSOP-14.
Common Dimensions
Symbol
Minimal (mm)
Nominal (mm)
Maximal (mm)
A
-
-
1.20
A1
0.05
-
0.15
b
0.19
-
0.30
D
4.90
-
5.10
e
0.65 BSC
E
-
6.40
-
E1
4.30
-
4.50
L
0.45
-
0.75
0
-
8
Copyright
2000, Austria Mikro Systeme International AG, Schlo Premsttten, 8141 Unterpremsttten, 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.
PDF 
ZIP