XE1205I074TRLF Просмотр технического описания (PDF) - Semtech Corporation

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XE1205I074TRLF

180 MHz – 1GHz Low-Power, High Link Budget Integrated UHF Transceiver

Semtech Corporation 

XE1205

8.5 REFERENCE CRYSTAL FOR THE FREQUENCY SYNTHESIZER

For narrow band applications, where users select the lowest frequency deviation and the narrowest baseband filter, the

crystal for reference oscillator of the frequency synthesizer should have the following typical characteristics:

Name

Fs

CL

Rm

Cm

C0

Δfs(0)

Δfs(ΔT)

Δfs(Δt)

Description

Nominal frequency

Min. value

-

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

-

Table 34: Crystal characteristics

Typ. value

39.0 MHz

(fundamental)

8 pF

-

-

-

-

-

-

Max. value

-

-

40Ω

30 fF

7 pF

10 ppm

10 ppm

5 ppm

The electrical specifications given in section 4.2.2 are valid for a crystal having the specifications given in Table 34. For

wide band applications requiring less frequency stability, the values for Δfs(0), Δfs(ΔT), and/or Δfs(Δt) can be relaxed. In

this case foffset + BWssb should be lower than BWfilter, where foffset is the offset (error) on the carrier frequency (the

sum of Δfs(0), Δfs(ΔT), and/or Δfs(Δt)), BWssb is the single side-band bandwidth of the signal, and BWfilter is the single

side-band bandwidth of the base-band filter.

The overtone crystal usage can result in higher oscillator start-up time than fundamental mode. The overtone crystal

should be designed for Cload = 8 to 10 pF and has parameters of Rm < 60Ω, C0 < 7 pF.

© Semtech 2008

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