ATA5811 Datasheet, PDF (15/90 Pages) ATMEL Corporation – UHF ASK/FSK TRANSCEIVER

ATA5811/ATA5812 [Preliminary]
DEM_OUT Output
RSSI Output
The data filter of the ATA5811/ATA5812 implies a quasi peak detector. This results in a
good suppression of the above mentioned disturbers and exhibits a good carrier to
Gaussian noise performance. The required useful signal to disturbing signal ratio to be
received with a BER of 10^-3 is less than 12 dB in ASK mode and less than 3 dB
(BR_Range_0 ... BR_Range_2)/6 dB (BR_Range_3) in FSK mode. Due to the many dif-
ferent waveforms possible these numbers are measured for signal as well as for
disturbers with peak amplitude values. Note that these values are worst case values and
are valid for any type of modulation and modulating frequency of the disturbing signal as
well as the receiving signal. For many combinations, lower carrier to disturbing signal
ratios are needed.
The internal raw output signal of the demodulator Demod_Out is available at pin
DEM_OUT. DEM_OUT is an open drain output and must be connected to a pull-up
resistor if it is used (typically 100 kΩ) otherwise no signal is present at that pin.
The output voltage of the pin RSSI is an analog voltage, proportional to the input power
level. Using the RSSI output signal, the signal strength of different transmitters can be
distinguished. The usable dynamic range of the RSSI amplifier is 70 dB, the input power
range P(RF_IN) is -115 dBm to -45 dBm and the gain is 8 mV/dB. Figure 12 shows the
RSSI characteristic of a typical device at 433.92 MHz with VS1 = VS2 = 2, 4 V to 3, 6 V
and T_amb = -40°C to +105°C with a matched input according to Table 2 on page 10 and
Figure 7 on page 10. At 868.3 MHz about 2.7 dB more signal level and at 315 MHz
about 1 dB less signal level is needed for the same RSSI results.
Figure 12. Typical RSSI Characteristic versus Temperature and Supply Voltage
1100
1000
900
800
700
Min.
600
500
Max.
Typ.
400
-120 -110 -100 -90 -80 -70 -60 -50 -40
P_{RF_IN} (dBm)
Frequency Synthesizer
The synthesizer is a fully integrated fractional-N design with internal loop filters for
receive and transmit mode. The XTO frequency f_XTO is the reference frequency FREF
for the synthesizer. The bits FR0 to FR8 in control registers 2 and 3 (see Table 20 on
page 35 and Table 23 on page 36) are used to adjust the deviation of f_XTO. In transmit
mode, at 433.92 MHz, the carrier has a phase noise of -111 dBC/Hz at 1 MHz and spu-
rious at FREF of -66 dBC with a high PLL loop bandwidth allowing the direct modulation
of the carrier with 20 kBaud Manchester data. Due to the closed loop modulation any
spurious caused by this modulation are effectively filtered out as can be seen in Figure
15 on page 17. In RX mode the synthesizer has a phase noise of -120 dBC/Hz at 1 MHz
and spurious of -75 dBC.
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4689B–RKE–04/04