ATA5423 ATMEL Corporation, ATA5423 Datasheet - Page 14

• Manufacturer Part Number: ATA5423
• Manufacturer: ATMEL Corporation

3.4
3.5
3.6
14
Frequency Accuracy of the Crystals
RX Supply Current versus Temperature and Supply Voltage
Blocking, Selectivity
ATA5423/25/28/29 [Preliminary]
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 band gap 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
Thus, the crystals used in the receiver and transmitter each need to be better than ±64.33 ppm
for 433.92 MHz and ±30.9 ppm for 868.3 MHz. 315, 345, 915MHz (TBD). In access control sys-
tems it may be advantageous to have a tighter tolerance at the base station in order to relax the
requirement for the remote control unit.
Table 3-5
supply voltage and temperature with VS = VS1 = VS2. As can be seen, the supply current at
2.4 V and –40°C is less than the typical supply current; this is useful because this is also the
operation point where a lithium cell has the worst performance. The typical supply current at
315 MHz, 345 MHz, 868.3 MHz or 915 MHz in RX mode is about the same as for 433.92 MHz
Table 3-5.
As can be seen in
higher than the sensitivity level in the presence of very large blockers of –47 dBm/–34 dBm with
small frequency offsets of ±1 ±10 MHz.
Figure 3-3
measurements were done with a signal of 433.92 MHz/FSK/20 kBaud/±16 kHz/ Manchester,
and with a level of -106 dBm + 3 dB = -103 dBm which is 3 dB above the sensitivity level. The
figures show how much larger than –103dBm a continuous wave signal can be before the BER
is higher than 10
page 11
-103 dBm + 56 dB = –47 dBm. These values, together with the good intermodulation perfor-
mance, avoid the need for a SAW filter in the remote control unit application.
VS = VS1 = VS2
T
T
T
Table 7-7 on page 39
amb
amb
amb
At 1 MHz, for example, the blocker can be 56 dB higher than –103 dBm which is
shows the typical supply current at 433.92 MHz of the transceiver in RX mode versus
= –
shows narrow band blocking and
=
=
25°C
85°C
40°C
Measured 433.92 MHz Receive Supply Current in FSK Mode
–3
. The measurements were done at the 50
Figure 3-3
±2.5 ppm = ±61.8 ppm for 868.3 MHz. 315, 345, 915 MHz (TBD).
±2.5 ppm = ±128.66 ppm for 433.92 MHz and
and
and
11.4 mA
8.4 mA
9.9 mA
2.4 V
Table 7-10 on page
Figure 3-4 on page
Figure 3-4
40). The XTO then has a remaining influ-
15, the receiver can receive signals 3 dB
wide band blocking characteristics. The
10.3 mA
11.9 mA
8.8 mA
3.0 V
input according to
12.4 mA
10.8 mA
9.2 mA
3.6 V
Figure 3-1 on
4841A–RKE–02/05