Atmel ATA8403
UHF ASK/FSK Industrial Transmitter
DATASHEET
Features
●
Integrated PLL loop filter
●
ESD protection also at ANT1/ANT2
(3.5kV HBM/150V MM; except pin 2: 4kV HBM/100V MM)
●
High output power (5.5dBm) with low supply current (8.5mA)
●
Modulation scheme ASK/FSK
●
FSK modulation is achieved by connecting an additional capacitor between the
XTAL load capacitor and the open drain output of the modulating microcontroller
●
Easy to design-in due to excellent isolation of the PLL from the PA and power
supply
●
Single Li-cell for power supply
●
Supply voltage 2.0V to 4.0V in the temperature range of –40°C to +85°C
●
Package TSSOP8L
●
Single-ended antenna output with high efficient power amplifier
●
CLK output for clocking the microcontroller
●
One-chip solution with minimum external circuitry
Applications
●
Industrial/aftermarket remote keyless entry systems
●
Alarm, telemetering, and energy metering systems
●
Remote control systems for consumer and industrial markets
●
Access control systems
●
Home automation
●
Home entertainment
●
Toys
4983C–INDCO–03/12
3.
General Description
This fully integrated PLL transmitter allows particularly simple, low-cost RF miniature transmitters to be assembled. The VCO is
locked to 64
×
f
XTAL
, and therefore a 13.5672MHz crystal is needed for a 868.3MHz transmitter and a 14.2969MHz crystal for a
915MHz transmitter. All other PLL and VCO peripheral elements are integrated.
The XTO is a series resonance oscillator so that only one capacitor together with a crystal connected in series to GND are
needed as external elements.
The crystal oscillator together with the PLL typically needs < 1ms until the PLL is locked and the CLK output is stable. There is
a wait time of
≥
4ms must be used until the CLK is used for the microcontroller and the PA is switched on.
The power amplifier is an open-collector output delivering a current pulse, which is nearly independent from the load
impedance. The delivered output power is therefore controllable via the connected load impedance.
This output configuration enables a simple matching to any kind of antenna or to 50Ω. A high power efficiency of
η=
P
out
/(I
S,PA
×
V
S
) of 24% for the power amplifier at 868.3MHz results when an optimized load impedance of
Z
Load
= (166 + j226)Ω is used at 3V supply voltage.
4.
Functional Description
If ENABLE = L and the PA_ENABLE = L, the circuit is in standby mode, consuming only a very small amount of current, so that
a lithium cell used as power supply can work for several years.
With ENABLE = H the XTO, PLL, and the CLK driver are switched on. If PA_ENABLE remains L, only the PLL and the XTO are
running and the CLK signal is delivered to the microcontroller. The VCO locks to 64 times the XTO frequency.
With ENABLE = H and PA_ENABLE = H the PLL, XTO, CLK driver, and the power amplifier are on. The power amplifier can be
switched on and off with PA_ENABLE. This is used to perform the ASK modulation.
4.1
ASK Transmission
The ATA8403 is activated by ENABLE = H. PA_ENABLE must remain L for t
≥
4ms, then the CLK signal can be taken to clock
the microcontroller, and the output power can be modulated by means of the PA_ENABLE pin. After transmission, PA_ENABLE
is switched to L, and the microcontroller switches back to internal clocking. The ATA8403 is switched back to standby mode with
ENABLE = L.
4.2
FSK Transmission
The ATA8403 is activated by ENABLE = H. PA_ENABLE must remain L for t
≥
4ms, then the CLK signal can be taken to clock
the microcontroller and the power amplifier is switched on with PA_ENABLE = H. The chip is then ready for FSK modulation.
The microcontroller starts to switch on and off the capacitor between the XTAL load capacitor and GND with an open-drain
output port, thus changing the reference frequency of the PLL. If the switch is closed, the output frequency is lower than if the
switch is open. After transmission PA_ENABLE is switched to L and the microcontroller switches back to internal clocking. The
ATA8403 is switched back to standby mode with ENABLE = L.
The accuracy of the frequency deviation with XTAL pulling method is about ±25% when the following tolerances are considered.
Figure 4-1. Tolerances of Frequency Modulation
V
S
C
Stray1
L
M
XTAL
C
M
R
S
C
Stray2
C
4
C
0
C
5
C
Switch
Using C
4
= 9.2pF ±2%, C
5
= 6.8pF ±5%, a switch port with C
Switch
= 3pF ±10%, stray capacitances on each side of the crystal of
C
Stray1
= C
Stray2
= 1pF ±10%, a parallel capacitance of the crystal of C
0
= 3.2pF ±10% and a crystal with C
M
= 13fF ±10%,
typically results in an FSK deviation of ±21.5kHz with worst case tolerances of ±16.8kHz to ±28.0kHz.
Atmel ATA8403 [DATASHEET]
4983C–INDCO–03/12
5
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