AS3933 datasheet(50/64 Pages) AMSCO

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[v1-08] 2015-Sep-02

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AS3933 − Detailed Description

Clock Generator

The Clock Generator can be based on a crystal oscillator

(R1<0>=1), the internal RC-oscillator (R1<0>=0), or an external

clock source (R1<0>=1). The crystal oscillator has higher

precision of the frequency with higher current consumption

and needs three external components (crystal plus two

capacitors). The RC-oscillator is completely integrated and can

be calibrated to increase its precision. Should a digital clock

already be available it can be applied directly to the XOUT pin

(XIN to VDD).

Regardless which clock generator is chosen, the frequency of

the Clock Generator must be set according to the carrier

frequency. Figure 56 shows the dependency of the Clock

Generator frequency from the carrier frequency and operating

frequency band.

Figure 56:

Clock Generator Frequency vs Frequency Band

It is possible to display the frequency of the clock generator on

the CL_DAT pin writing R2<3:2>=11 and R16<7>=1.

Carrier Frequency

[kHz]

Clock Generator Frequency

15 – 23

23-40

40-65

65 – 95

95 - 150

fRC

fcarr

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⋅

fRC

fcarr

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⋅

fRC

fcarr

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⋅

fRC

fcarr

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⋅

fRC

fcarr

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