ATA5811-PLQX Atmel, ATA5811-PLQX Datasheet - Page 12

• Manufacturer Part Number: ATA5811-PLQX
• Manufacturer: Atmel

Specifications of ATA5811-PLQX

• 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

Frequency Accuracy of the
Crystals
RX Supply Current versus
Temperature and Supply
Voltage
Blocking, Selectivity
12
ATA5811/ATA5812 [Preliminary]
As can be seen in Figure 8 on page 11 the supply voltage has almost no influence. The
temperature 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 frequency 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 fre-
quency correction 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 how-
ever, 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 “Digital Control Logic”).
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 Table 20 on page 35 and Table 23 on page 36). The XTO
then has a remaining influence of less than ±2 ppm over temperature and supply volt-
age due to the bandgap controlled gm of the XTO.
The needed frequency stability of the used crystals over temperature and aging is hence
± 5 8 k H z /4 3 3 .9 2 MH z - 2
±58 kHz/868.3 MHz - 2
tals in 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 shows the typical supply current at 433.92 MHz of the transceiver in RX mode
versus supply voltage and temperature with VS = VS1 = VS2. As you can see the sup-
ply current at 2.4 V 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 sup-
ply current at 315 MHz or 868.3 MHz in RX mode is about the same as for 433.92 MHz.
Table 5. Measured 433.92 MHz Receive Supply Current in FSK Mode
As can be seen in Figure 9 on page 13 and Figure 10 on page 13, the receiver can
receive signals 3 dB higher than the sensitivity level in presence of very large blockers
of -47 dBm/-34 dBm with small frequency offsets of 1 10 MHz.
T
T
T
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 kBaud.
VS =
=
=
=
105°C
-40°C
25°C
±2.5 ppm = ±61.8 ppm for 868.3 MHz. Thus, the used crys-
11.4 mA
8.4 mA
9.9 mA
2.4 V
± 2. 5 pp m = ± 1 28 .6 6 p pm fo r 4 33 . 92 M Hz a n d
10.3 mA
11.9 mA
8.8 mA
3.0 V
10.8 mA
12.4 mA
9.2 mA
4689B–RKE–04/04
3.6 V