Rainbow Electronics ATA5812 - Manual (Page 16)

16
ATA5811/ATA5812 [Preliminary]
4689B–RKE–04/04
The initial tolerances of the crystal oscillator due to crystal tolerances, internal capacitor
tolerances and the parasitics of the board have to be compensated at manufacturing
setup with control registers 2 and 3 as can be seen in Table 12 on page 24. The other
control words for the synthesizer needed for ASK, FSK and receive/transmit switching
are calculated internally. The RF (Radio Frequency) resolution is equal to the XTO fre-
quency divided by 16384 which is 777.1 Hz at 315.0 MHz, 808.9 Hz at 433.92 MHz and
818.59 Hz at 868.3 MHz.
FSK/ASK Transmission Due to the fast modulation capability of the synthesizer and the high resolution, the car-
rier can be internally FSK modulated which simplifies the application of the transceiver.
The deviation of the transmitted signal is ±20 digital frequency steps of the synthesizer
which is equal to ±15.54 kHz for 315 MHz, ±16.17 kHz for 433.92 MHz and ±16.37 kHz
for 868.3 MHz.
Due to closed loop modulation with PLL filtering the modulated spectrum is very clean,
meeting ETSI and CEPT regulations when using a simple LC filter for the power ampli-
fier harmonics as it is shown in Figure 5 on page 7. In ASK mode the frequency is
internally connected to the center of the FSK transmission and the power amplifier is
switched on and off to perform the modulation. Figure 13 to Figure 15 on page 17 show
t h e s p e c t r u m o f t h e F S K m o d u l a t i o n w i t h p s e u d o r a n d o m d a t a w i t h
20 kBaud/±16.17 kHz/Manchester and 5 dBm output power.
Figure 13. FSK-modulated TX Spectrum (20 kBaud/
±
16.17 kHz/Manchester Code)
Ref 10 dBm Atten 20 dB
Samp
Log
10
dB/
VAvg
5 0
W1 S2
S3 FC
Center 433.92 MHz
Res BW 100 kHz VBW 100 kHz
Span 30 MHz
Sweep 7.5 ms (401 pts)