MT9040 데이터 시트보기 (PDF) - Zarlink Semiconductor Inc

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MT9040

T1/E1 Synchronizer

Zarlink Semiconductor Inc 

MT9040

Data Sheet

MT9040

OSCi

1MΩ

20MHz

56pF

39pF 3-50pF

OSCo

100Ω

1uH

1uH inductor: may improve stability and is optional

Figure 6 - Crystal Oscillator Circuit

The accuracy of a crystal oscillator depends on the crystal tolerance as well as the load capacitance tolerance.

Typically, for a 20MHz crystal specified with a 32pF load capacitance, each 1pF change in load capacitance

contributes approximately 9ppm to the frequency deviation. Consequently, capacitor tolerances, and stray

capacitances have a major effect on the accuracy of the oscillator frequency.

The trimmer capacitor shown in Figure 6 may be used to compensate for capacitive effects. If accuracy is not a

concern, then the trimmer may be removed, the 39pF capacitor may be increased to 56pF, and a wider tolerance

crystal may be substituted.

The crystal should be a fundamental mode type - not an overtone. The fundamental mode crystal permits a simpler

oscillator circuit with no additional filter components and is less likely to generate spurious responses. The crystal

specification is as follows.

Frequency:

20MHz

Tolerance:

As required

Oscillation Mode:

Fundamental

Resonance Mode:

Parallel

Load Capacitance:

32pF

Maximum Series Resistance:

35Ω

Approximate Drive Level:

1mW

e.g., R1B23B32-20.0MHz

(20ppm absolute, ±6ppm 0C to 50C, 32pF, 25Ω)

11

Zarlink Semiconductor Inc.

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