In order to consider the measure against abnormal oscillation, it is important to consider the cause first.
- Parasitic oscillation (spurious oscillation) of CERALOCK®
- Improper circuit wiring or timing error (CR/LC oscillation, ring oscillation)
In order to distinguish 1 from 2 above, replace the CERALOCK® with a capacitor (Cx) with the same capacitance as the CERALOCK®. In case of Type 2, the circuit can provide normal oscillation even if the CERALOCK® is replaced by Cx.
After finding the cause of abnormal oscillation, you must take appropriate countermeasures:
Countermeasure against Type 1
will develop many kinds of parasitic oscillations (spurious oscillations) in addition to the oscillation with the target frequency (main oscillation frequency). If the oscillation circuit is operated with improper circuit constants, parasitic oscillations may occur. Commonly observed spurious modes are listed in Table 1.
Table 1 Examples of spurious oscillation frequencies by series
|Abnormal oscillation frequency/mode
|Triple of rated frequency/Triple wave
|CSTCW/CSACW_X Series (*1)
|One third of rated frequency/Fundamental wave
|CSTCW/CSACW_X Series (*1)
|Five thirds of rated frequency/Quintuple wave
Among the CERALOCK® Series listed in the above table, (1)and (2b) will develop oscillations at a higher frequency than the main frequency. To lower the gain in high frequency range, you can take the following measures:
a.Increase "CL" (CL1=CL2) (approx. two steps under the E6 system).
b.Add "Rd" (damping resistor: 100 to 10k ohms).
If you use a), the oscillation frequency will slightly decrease, and you need to consider the influence on the sets.
If "CL" and "Rd" are increased too much in case of both a) and b), oscillation will stop.
In case of (2a), the CERALOCK® will develop oscillations at a lower frequency than the main frequency. Therefore, you must increase the gain in the high frequency range, or lower the gain in the low frequency range by taking the following measures:
c.Lower "CL" (CL1=CL2) (approx. three steps under the E6 system).
d.Add "Rp" (approx. 1 to 100k ohms), or lower "Rf."
If "CL" is reduced too much in case of c), oscillation becomes unstable. If "Rf" is reduced too much in case of d), oscillation will stop.
Countermeasure against Type 2
The following example shows an abnormal oscillation in a circuit where the CERALOCK® serves as a capacitor. We have not established a fixed countermeasure against this type of abnormal oscillation, because an effective method varies depending on the IC being used. However, the following countermeasures can be considered:
f.Make "CL1" and "CL2" unbalanced.
*1) CSTCW/CSACW Series
Not recommended for new designs. We are evaluating the schedule for the discontinuing of production of this item.
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