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Analysis of the Function of Ceramic Resonator Oscillating Circuit Components

Ceramic resonator oscillation circuit elements include: feedback resistors, damping resistors, loading capacitors, bias resistors. The functions of these components are described below.

The effect of the circuit parameters is as follows:

Analysis of the Function of Ceramic Resonator Oscillating Circuit Components

Rf: feedback resistor

The feedback resistor determines the biasing of the oscillator circuit. Under normal circumstances, the feedback resistance used in C-MOS integrated circuits is between 100KΩ and 10MΩ (usually 1MΩ), while the feedback resistance used in TTL integrated circuits is between 1KΩ and 10KΩ (usually 4.7KΩ). The reason is that The I/O impedance of TTL integrated circuits is low. If the feedback resistance is too large, the amount of feedback will be reduced, resulting in unstable operating point. If the feedback resistor is too small, it will result in a decrease in gain or an increase in current. Currently, feedback resistors are used in most integrated circuits.

Rd: Damping Resistor

Damping resistors and loading capacitors can act as low-pass filters to suppress abnormal harmonic oscillations by reducing gain in the high frequency range. In addition, the IC gain can also be limited to better match the CERALOCK® with the IC, thereby suppressing unwanted ringing, overshoot, and undershoot. In the kHz band, the damping resistance should be several thousand ohms, and in the MHz band, the damping resistance should be between tens of ohms and hundreds of ohms. Optional damping resistor is available.

CL1/CL2: Load capacitors

This parameter is critical for determining the stability of the oscillator circuit. If the load capacitance is too small, the oscillation waveform will be deformed, resulting in unstable oscillation. Conversely, if the load capacitance is too large, the oscillation stops. Compared with the same integrated circuit, the oscillation circuit will generate lower frequency and require larger electrostatic capacity.

Rb: Bias Resistor

If the gain of the integrated circuit is too large or a TTL, three-phase buffer integrated circuit is used, in order to reduce the gain of the integrated circuit or suppress unstable oscillation, a bias resistor can be used to change the bias point purposefully. C-MOS ICs use 1MΩ to 10MΩ bias resistors, and TTL uses 1KΩ to 10KΩ bias resistors.

The constants are different for different ICs and CERALOCK®.

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