XE1202A View Datasheet(PDF) - Semtech Corporation

Part Name

Description

Manufacturer

XE1202A

433 MHz / 868 MHz / 915 MHz Low-Power, Integrated UHF Transceiver

Semtech Corporation 

XE1202A TrueRF™

6.4 Loop filter of the frequency synthesizer

The loop filter of the frequency synthesizer is shown in Figure 17 below:

LFB

RL1

CL2

XE1202A

TrueRF™

CL1

VSS

Figure 17: Loop filter of the frequency synthesizer

The recommended values for the external components are given in the following table:

Name

CL1

CL2

RL1

434 MHz

22 nF ± 10 %

1 nF ± 5 %

0.56 kΩ ± 5 %

869 MHz

22 nF ± 10 %

1 nF ± 5 %

0.47 kΩ ± 5 %

915 MHz

22 nF ± 10 %

1 nF ± 5 %

0.47 kΩ ± 5 %

Table 29: loop filter component values

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:

Name

Fs

Description

Nominal frequency

Min. value

-

CL

Rm

Cm

C0

∆fs(0)

∆fs(∆T)

∆fs(∆t)

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

-

Typ. Value

39.0 MHz

(fundamental)

8 pF (*)

-

-

-

-

-

Max. value

-

-

40 Ω

30 fF

7 pF (*)

10 ppm

10 ppm

-

5 ppm

Table 30: Recommended crystal characteristics

(*) 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 fOFFSET + BWssb should be lower than

BBW, where fOFFSET is the offset (error) from the carrier frequency (the sum of ∆fs(0), ∆fs(∆T), and/or ∆fs(∆t)),

© Semtech 2006

30

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