ATA5811_06 ATMEL [ATMEL Corporation], ATA5811_06 Datasheet - Page 12

• Manufacturer Part Number: ATA5811_06
• Description: UHF ASK/FSK TRANSCEIVER
• Manufacturer: ATMEL [ATMEL Corporation]

5.4
5.5
12
Frequency Accuracy of the Crystals
RX Supply Current versus Temperature and Supply Voltage
ATA5811/ATA5812
As can be seen in
perature has an influence of about +1.5/–0.7 dB and a frequency offset of ±65 kHz also
influences by about ±1 dB. All these influences, combined with the sensitivity of a typical IC, are
then within a range of –103.7 dBm and –107.3 dBm over temperature, supply voltage and fre-
quency offset which is –105.5 dBm ±1.8dB. The integrated IF filter has an additional production
tolerance of only ±7 kHz, hence, a frequency offset between the receiver and the transmitter of
±58 kHz can be accepted for XTAL and XTO tolerances.
Note:
This small sensitivity spread over supply voltage, frequency offset and temperature is very
unusual in such a receiver. It is achieved by an internal, very fast and automatic frequency cor-
rection in the FSK demodulator after the IF filter, which leads to a higher system margin. This
frequency correction tracks the input frequency very quickly, if however, the input frequency
makes a larger step (e.g., if the system changes between different communication partners), the
receiver has to be restarted. This can be done by switching back to Idle mode and then again to
RX mode. For that purpose, an automatic mode is also available. This automatic mote switches
to Idle mode and back into RX mode every time a bit error occurs (see section
Logic” on page
The XTO is an amplitude regulated Pierce oscillator with integrated load capacitors. The initial
tolerances (due to the frequency tolerance of the XTAL, the integrated capacitors on XTAL1,
XTAL2 and the XTO’s initial transconductance gm) can be compensated to a value within
±0.5 ppm by measuring the CLK output frequency and programming the control registers 2 and
3 (see
ence of less than ±2 ppm over temperature and supply voltage due to the bandgap controlled
gm of the XTO.
The needed frequency stability of the used crystals over temperature and aging is hence
±58 kHz/433.92 MHz – 2
±58 kHz/868.3 MHz – 2
receiver and transmitter each need to be better than ±64.33 ppm for 433.92 MHz and
±30.9 ppm for 868.3 MHz. In access control systems it may be advantageous to have a more
tight tolerance at the base-station in order to relax the requirement for the key fob.
Table 5-5
supply voltage and temperature with VS = VS1 = VS2. As you can see the supply current at 2.4V
and –40°C is less than the typical one which helps because this is also the operation point
where a lithium cell has the worst performance. The typical supply current at 315 MHz or
868.3 MHz in RX mode is about the same as for 433.92 MHz.
Table 5-5.
T
T
T
Table 9-7 on page 36
amb
amb
amb
For the demodulator used in the ATA5811/ATA5812, the tolerable frequency offset does not
change with the data frequency, hence, the value of ±58 kHz is valid for up to 1 Kbit/s.
VS =
shows the typical supply current at 433.92 MHz of the transceiver in RX mode versus
=
=
=
–40°C
105°C
25°C
Measured 433.92 MHz Receive Supply Current in FSK Mode
33).
Figure 5-2 on page 11
±2.5 ppm = ±61.8 ppm for 868.3 MHz. Thus, the used crystals in
±2.5 ppm = ±128.66 ppm for 433.92 MHz and
and
11.4 mA
8.4 mA
9.9 mA
2.4 V
Table 9-10 on page
the supply voltage has almost no influence. The tem-
36). The XTO then has a remaining influ-
10.3 mA
11.9 mA
8.8 mA
3.0 V
12.4 mA
10.8 mA
“Digital Control
9.2 mA
3.6 V
4689F–RKE–08/06