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.
R
f
Frequency range
Values of check resistance
3.5 to 4.5MHz
4.6 to 6.0MHz
1.5k
1.0k
800
500
400
R
sup
6.1 to 10.0MHz
10.1 to 14.0MHz
14.1 to 20.0MHz
C
1
C
2
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.
1
1 to CLMAX.
1
1
C2
1
C3
1
1
C2
1
C3
CLMIN.
C1CT
C1CT
When these calculation results are substituted for the following equation for load resonance frequency, the oscillation
frequency can be obtained.
C1
fL fs
1
2 (C0CL)
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KYOCERA AVX [ KYOCERA AVX ]
