When a device does not operate normally, the following four factors are attributable to the oscillation circuit.
- Not oscillating or the oscillation stops (oscillation is not sustained).
- The oscillation frequency deviates from the standard value.
- The oscillation amplitude is insufficient.
- The temperature characteristics of the oscillation frequency are abnormal.
In many cases, this occurs due to the configuration of the circuit conditions and component constants.
First, check the oscillation state, frequency, and amplitude, etc., and verify whether the circuit conditions and microcontroller settings are appropriate.
When confirming if there is a problem with the oscillation circuit, isolate the causes more easily by checking in the following order.
- Check whether it is oscillating.
Measure the oscillation waveform with an oscilloscope, etc. to confirm if oscillation has started.
- Check the oscillation frequency.
Check if the oscillation frequency matches the standard value.
- Check the oscillation amplitude.
Check if there is sufficient amplitude. If the amplitude is small, the circuit conditions may be inappropriate.
- Check the circuit conditions.
Check if the load capacitance, limiting resistance, and microcontroller settings, etc. match the specifications of the crystal unit.
<Not oscillating or the oscillation stops>
The oscillation circuit has not started, and the clock signal is not being generated.
Because the clock is not being supplied, it causes the microcontroller and the entire system to fail to operate.
Main factors:
- Improper microcontroller settings
- Insufficient oscillation margin
- Mismatch between the circuit conditions and the crystal unit specifications
For countermeasures, refer to “What are the causes and countermeasures when a crystal unit oscillation circuit does not oscillate?”
<Oscillation frequency deviates from the standard value>
If the oscillation frequency deviates from the standard value, it may impact the microcontroller processing and communication timing.
Main factors:
- Mismatch between the load capacitance on the oscillation circuit side and the rated load capacitance of the oscillator
- Deviation of the drive level from the specification standard value
- Abnormal oscillation
For countermeasures, refer to “What are the causes and countermeasures for deviation in the oscillation frequency of a crystal unit?”
<Oscillation amplitude is insufficient>
If the amplitude is small, the clock signal may not be correctly recognized, which can cause the oscillation circuit to fail to start up or operate in an unstable manner.
Main factors:
- The limiting resistance value is too large.
- The load capacitance value is not appropriate.
For countermeasures, refer to “If small oscillation amplitude will be a cause of trouble in oscillation circuit?”
<Temperature characteristics of the oscillation frequency are abnormal>
The frequency may fluctuate more than usual in response to temperature changes.
Main factors:
- Deviation of the drive level from the standard value
- Deviation of the oscillator characteristics from the standard values
- Temperature-dependent characteristics of the circuit components
For countermeasures, refer to “It seems that oscillation frequency drift by temperature is not normal. What is a cause?”
When checking for oscillation circuit problems, it is helpful to verify the following items.
- Check the microcontroller settings
- Ensure sufficient oscillation margin (as a general guideline, 5x or more of the R1 standard value for consumer applications and 10x or more for automotive applications)
- Adjust the load capacitance
- Adjust the limiting resistance and optimize the amplitude and drive level
- Check the drive level is within the specification range
Explanation of technical terms
What is oscillation margin?
It is an index that indicates the amount of margin required for an oscillation circuit to start and maintain oscillation.
It is generally recommended to ensure a margin of 5x or more for consumer applications and 10x or more for automotive applications relative to the standard value of the equivalent series resistance (R1) of the oscillator.
For the measurement method of the oscillation margin, refer to “Basic Knowledge of How to Measure the Oscillation Margin”
What is drive level?
Drive level indicates the power consumed by the crystal unit.
If the drive level is too high, it may cause abnormalities in the frequency-temperature characteristics.
For drive level measurement methods, refer to “Basic Knowledge of How to Measure the Drive Level”
What is load capacitance?
It is the capacitive component connected to the oscillation circuit.
The load capacitance impacts the oscillation frequency and stability (oscillation margin) of the oscillation circuit.
For the load capacitance, refer to “Crystal Units: Basic Knowledge of Technical Terms.”
Scenarios where this information is useful
During the design process
It serves as a reference when considering component constants and circuit conditions of the oscillation circuit.
During prototyping and evaluation
It can be used as a checkpoint when confirming the oscillation state and frequency characteristics of prototypes.
Troubleshooting
It can be helpful when checking if the oscillation circuit is the cause when the device does not start normally or when communication errors occur.
Mass production defects
It serves as a reference for investigating the causes of malfunctions and variations occurring in mass-produced units.