XE1202AI027TRLF Semtech, XE1202AI027TRLF Datasheet - Page 29

• Manufacturer Part Number: XE1202AI027TRLF
• Description: Narrow Band 433/868/915MHz RF Transceiver
• Manufacturer: Semtech

6.4 Loop filter of the frequency synthesizer
The loop filter of the frequency synthesizer is shown in Figure 17 below:
The recommended values for the external components are given in the following table:
6.5 Reference crystal for the frequency synthesizer
For narrow band applications, (lowest frequency deviation and the narrowest baseband filter), the crystal for
reference oscillator of the frequency synthesizer should have characteristics as shown in Table 30:
(*) The on-chip oscillator is implemented in two selectable versions: the first for CL = 8 pF and C0 = 7 pF, and the
second for CL = 8 pF and C0 = 3 pF; the latter will allow larger amplitude for the internal signal with slightly lower
power consumption.
The electrical specifications given in Section 3.2.2 are valid provided the crystal satisfies the specifications given in
Table 30.
For less demanding applications (wider signal bandwidth and/or reduced temperature range), it is possible to use a
crystal with larger values for ∆fs(0), ∆fs(∆T), and/or ∆fs(∆t). In this case f
BBW, where f
© Semtech 2006
Name
Fs
CL
Rm
Cm
C0
∆fs(0)
∆fs(∆T)
∆fs(∆t)
OFFSET
Description
Nominal frequency
Load capacitance for fs (on-chip)
Motional resistance
Motional capacitance
Shunt capacitance
Calibration tolerance at 25 °C
Stability over temperature range
(-40 °C to 85 °C)
Aging tolerance in first 5 years
is the offset (error) from the carrier frequency (the sum of ∆fs(0), ∆fs(∆T), and/or ∆fs(∆t)),
Name
CL1
CL2
RL1
CL1
Figure 17: Loop filter of the frequency synthesizer
RL1
Table 30: Recommended crystal characteristics
0.56 kΩ ± 5 %
22 nF ± 10 %
1 nF ± 5 %
Table 29: loop filter component values
434 MHz
VSS
30
CL2
0.47 kΩ ± 5 %
22 nF ± 10 %
1 nF ± 5 %
Min. value
-
-
-
-
-
-
-
-
869 MHz
XE1202A TrueRF™
LFB
XE1202A
TrueRF™
Typ. Value
39.0 MHz
(fundamental)
8 pF (*)
-
-
-
-
-
-
OFFSET
0.47 kΩ ± 5 %
22 nF ± 10 %
1 nF ± 5 %
915 MHz
+ BWssb should be lower than
Max. value
-
-
40 Ω
30 fF
7 pF (*)
10 ppm
10 ppm
5 ppm
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