Failure case 1: Non-oscillation
There is a possibility of non-oscillation mainly in the following cases

1.When negative resistance is insufficient
As a related matter, please refer to "What is Negative resistance (1)＜Overview and Target Values of NDK＞".
2.When there is no appropriate feedback resistor (Rf) in the circuit
If a feedback resistor (Rf) is built into the IC, it is unnecessary to have an external feedback resistor (Rf) as shown in Fig. 1.

3.When the unit is operated to outside of the temperature range specified by the crystal unit or IC.
4.When parts are not mounted properly in the circuit

Failure Case 2: Deviation of the oscillation frequency
In the following cases, oscillation may not occur at the proper oscillation frequency.

1. When there is a large difference between the circuit load capacity and the load capacity specification of the crystal unit.
As a related matter, please refer to the difference of oscillation frequency (3) ＜improvement method＞.
2.When temperature characteristics of the crystal unit are not considered
As a related matter, please Refer to Temperature Characteristics (1) ＜Difference in Oscillation Frequency＞
3.When parts are not mounted properly in the circuit
4. When the internal settings of the IC are not appropriate
Since the circuit characteristics can vary depending on the internal settings of the IC, inappropriate settings may cause a shift in the oscillation frequency.

Failure Case 3: Oscillation does not occur in normal mode
This is a case of "it is necessary to oscillate with a fundamental wave, but it oscillates with a third-order overtone."
For details, refer to "What is Negative Resistance (5) ＜Tertiary Overtone Characteristics＞

Failure Case 4: Oscillation voltage level is not appropriate
If the actual oscillation voltage level is higher or lower than the level required by the circuit, it may cause problems in the overall operation of the circuit.
The main factors that affect the oscillation voltage level are as follows:
• Circuit constants (such as the component values used at points like Cin, Cout, and Rd in Fig. 1)
• Internal settings of the IC
• VDD voltage

For the appropriate oscillation voltage level for each circuit, please contact the manufacturer of the IC used in that circuit.