ATA8401 ATMEL Corporation, ATA8401 Datasheet - Page 4

• Manufacturer Part Number: ATA8401
• Manufacturer: ATMEL Corporation

3. General Description
4. Functional Description
4.1
4.2
4
ASK Transmission
FSK Transmission
ATA8401
This fully integrated PLL transmitter allows particularly simple, low-cost RF miniature transmit-
ters to be assembled. The VCO is locked to 32 f
needed for a 315 MHz 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 con-
nected in series to GND are needed as external elements.
The crystal oscillator together with the PLL typically needs < 3 ms until the PLL is locked and the
CLK output is stable. There is a wait time of
and the PA is switched on.
The power amplifier is an open-collector output delivering a current pulse, which is nearly inde-
pendent 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 50 . A high
power efficiency of = P
load impedance of Z
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 32 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.
The ATA8401 is activated by ENABLE = H. PA_ENABLE must remain L for typically
then the CLK signal can be taken to clock the microcontroller and the output power can be mod-
ulated by means of the PA_ENABLE pin. After transmission, PA_ENABLE is switched to L and
the microcontroller switches back to internal clocking. The ATA8401 is switched back to standby
mode with ENABLE = L.
The ATA8401 is activated by ENABLE = H. PA_ENABLE must remain L for typically
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 microcon-
troller 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 ATA8401 is
switched back to standby mode with ENABLE = L.
The accuracy of the frequency deviation with XTAL pulling method is about ±25% when the fol-
lowing tolerances are considered.
Load
= (255 + j192)
out
/(I
S,PA
V
S
) of 40% for the power amplifier results when an optimized
is used at 3V supply voltage.
3 ms until the CLK is used for the microcontroller
XTAL
, and therefore a 9.8438 MHz crystal is
4984A–IND–02/07
3 ms,
3 ms,