Oscillation circuit may develop abnormal oscillation by itself, depending on the circuit type. To differentiate the abnormal oscillation attributed to the oscillation circuit from the spurious oscillation of the CERALOCK®
, you must take a reading of a frequency counter to check if the reading is equal to the frequency of the spurious oscillation mode, or change the power supply voltage to check if there is a large change in frequency (+/-1% or more).
The following table lists examples of frequently observed abnormal oscillations.
|Type of oscillation
||When the IC gain is high, CR oscillation occurs depending on the electrostatic capacitance (Cf) and load capacitance (CL) of the CERALOCK®, and the internal resistance (R) of the IC. The frequency varies with a change in power supply voltage.
||When the IC gain is high, LC oscillation occurs depending on the conductance (C) and inductance (L) of the wiring (Mostly, the oscillation frequency is 10MHz or higher). The frequency varies with a change in wiring.
||Ring oscillation is caused by delay of the time constant used in the multistage inverter-type IC (Mostly, the oscillation frequency is 10MHz or higher).
Checking presence/absence of abnormal oscillation
You can check if the circuit develops abnormal oscillation by using the following methods:
A.Change the power supply voltage or circuit constants during measurement at oscillation start.
If abnormal oscillation occurs, the waveform immediately after oscillation start becomes unstable.
B.Turn on/off the power supply.
When the power supply is turned on, abnormal oscillation occurs.
C.Raise the power supply voltage gradually
This method is effective for resonators using 3rd-overtone frequency such as the CSTCW/CSACW_X Series (*1). When the power supply voltage is low, oscillation starts with the fundamental wave. However, the fundamental wave may be retained after the power supply voltage reaches the target voltage.
D.Raise or lower the operating temperature by using a dryer or freezer.
While the circuit is cooled or warmed, it may easily develop abnormal oscillation.
*1) CSTCW/CSACW Series
Not recommended for new designs. We are evaluating the schedule for the discontinuing of production of this item.