CX-2520SB Ver la hoja de datos (PDF) - Kyocera Kinseki Corpotation

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CX-2520SB

Crystal Units Surface Mount Type

Kyocera Kinseki Corpotation 

Handling Notes

(5) Method of checking oscillation circuit

①Some ICs have a low upper-limit value of usable frequency, so refer to individual IC catalog to make sure that the IC can

oscillate a crystal unit with an adequate negative resistance.

②The following figure shows an example of a CMOS oscillation circuit. Check resistance Rsup is connected in series with

the crystal unit to check the negative resistance. Use 3 to 22pF for C1 and C2, and see the table below for values of check

resistance.

Rf

Rsup

C1

C2

Frequency range

3.5 to 4.5MHz

4.6 to 6.0MHz

6.1 to 10.0MHz

10.1 to 14.0MHz

14.1 to 20.0MHz

Values of check resistance

1.5k

1.0k

800

500

400

③Using a spectrum analyzer or oscilloscope, check that every oscillation is normally activated while turning the power on

and off several times. For oscillation circuits with no power regulator ICs, carefully check changes in the negative

resistance against supply voltage and in frequencies.

④When oscillation is normal, remove the check resistance before using the crystal circuit.

⑤If oscillation is unstable or is not generated, gradually decrease the values of C1 and C2 until normal oscillation is obtained.

⑥If normal oscillation cannot be generated near 10MHz or near 20MHz, replace the IC with a new one suitable for higher

frequencies.

(6) Load capacitance and oscillation frequency of transistor/fundamental crystal oscillation circuit

Viewed from the connection terminals of a crystal unit, the load capacitance CL of an oscillation circuit is generally comprised

of C1, Ct, C2, and C3 if stray capacitance of the circuit and the capacitance between base and emitter of the transistor are

ignored. Since trimmer capacitor is adjusted to CT = MIN. to MAX. for zero adjustment of the oscillation frequency, the value

of CL at this time can be obtained from the following equation.

CLMIN. 

1

C1CT



1

C2



1

C3

1

to CLMAX.

1

C1CT



1

C2



1

C3

1

When these calculation results are substituted for the following equation for load resonance frequency, the oscillation

frequency can be obtained.

fL  fs

2

C1

(C0 CL)

1

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