ATA5812-PLQW Atmel, ATA5812-PLQW Datasheet - Page 9

• Manufacturer Part Number: ATA5812-PLQW
• Manufacturer: Atmel

Specifications of ATA5812-PLQW

• Operating Temperature (min): -40C
• Operating Temperature (max): 105C
• Operating Temperature Classification: Industrial
• Product Depth (mm): 7mm
• Product Height (mm): 0.9mm
• Product Length (mm): 7mm
• Lead Free Status / Rohs Status: Compliant

5. RF Transceiver
5.1
4689F–RKE–08/06
Low-IF Receiver
According to
PA (Power Amplifier), RX/TX switch, fractional-N frequency synthesizer and the signal process-
ing part with mixer, IF filter, IF amplifier, FSK/ASK demodulator, data filter and data slicer.
In receive mode the LNA pre-amplifies the received signal which is converted down to 226 kHz,
filtered and amplified before it is fed into an FSK/ASK demodulator, data filter and data slicer.
The RSSI (Received Signal Strength Indicator) signal and the raw digital output signal of the
demodulator are available at the pins RSSI and DEM_OUT. The demodulated data signal
Demod_Out is fed to the digital control logic where it is evaluated and buffered as described in
section
In transmit mode the fractional-N frequency synthesizer generates the TX frequency which is fed
to the PA. In ASK mode the PA is modulated by the signal PA_Enable. In FSK mode the PA is
enabled and the signal TX_DATA (FSK) modulates the fractional-N frequency synthesizer. The
frequency deviation is digitally controlled and internally fixed to about ±16 kHz (see
page 25
Control Logic” on page
will only start if the synthesizer is locked.
The RX/TX switch can be used to combine the LNA input and the PA output to a single antenna
with a minimum of losses.
Transparent modes without buffering of RX and TX data are also available to allow protocols
and coding schemes other than the internal supported Manchester encoding.
The receive path consists of a fully integrated low-IF receiver. It fulfills the sensitivity, blocking,
selectivity, supply voltage and supply current specification needed to manufacture an automo-
tive key fob without the use of SAW blocking filter (see
be connected to the roof antenna in the car when using an additional blocking SAW front-end fil-
ter as shown in
At 433.92 MHz the receiver has a typical system noise figure of 7.0 dB, a system I1dBCP of
-30 dBm and a system IIP3 of –20 dBm. There is no AGC or switching of the LNA needed, thus,
a better blocking performance is achieved. This receiver uses an IF (Intermediate Frequency) of
226 kHz, the typical image rejection is 30 dB and the typical 3 dB IF filter bandwidth is 185 kHz
(f
signal to Gaussian noise ratio of 8 dB for 20 Kbit/s Manchester with ±16 kHz frequency deviation
in FSK mode, thus, the resulting sensitivity at 433.92 MHz is typically –106 dBm at 20 Kbit/s
Manchester.
Due to the low phase noise and spurious of the synthesizer in receive mode
eighth order integrated IF filter the receiver has a better selectivity and blocking performance
than more complex double superhet receivers but without external components and without
numerous spurious receiving frequencies.
A low-IF architecture is also less sensitive to second-order intermodulation (IIP2) than direct
conversion receivers where every pulse or AM-modulated signal (especially the signals from
TDMA systems like GSM) demodulates to the receiving signal band at second-order
non-linearities.
Note:
IF
= 226 kHz ±92.5 kHz, f
“Digital Control Logic” on page
1. –120 dBC/Hz at ±1 MHz and –75 dBC at ±FREF at 433.92 MHz
for exact values). The transmit data can also be buffered as described in section
Figure 1-3 on page
Figure 3-1 on page
33. A lock detector within the synthesizer ensures that the transmission
lo_IF
= 133.5 kHz and f
5, the RF transceiver consists of an LNA (Low-Noise Amplifier),
7.
33.
hi_IF
= 318.5 kHz). The demodulator needs a
Figure 2-1 on page
ATA5811/ATA5812
6). The receiver can
(1)
together with the
Table 6-1 on
“Digital
9