Analysis of the differences, advantages and disadvantages between resonators and oscillators

       Resonators and oscillators are often confused. After some time of comparison, I have sorted them out. We are used to calling them crystal oscillators, but this term is actually very vague. Here, the active ones are called oscillators, and the passive ones are called resonators.

　　Resonator​

　　An electronic component that generates a resonant frequency. It is a typical passive device that requires an external circuit to drive it to work and generate a clock output.

　　Oscillator​

　　It is an energy conversion device that converts DC power into AC power with a certain frequency. The circuit it constitutes is called an oscillation circuit. The oscillator is an active device, and the oscillator has an additional control circuit compared to the resonator.

　　From left to right in the picture: crystal resonator, ceramic resonator, crystal oscillator, silicon oscillator.

　　Crystal resonator [QUARTZ CRYSTAL UNITS] [CRYSTAL]

　　Quartz crystal, commonly known as crystal, is composed of SIO2 and is an important piezoelectric material. Its main feature is that its atoms or molecules are arranged regularly, which is reflected in the symmetry of the shape on a macro scale. Under the action of the electric field, stress is generated inside the crystal and it deforms, thereby generating mechanical vibration and obtaining a specific frequency. This inverse piezoelectric effect is used to manufacture quartz crystal resonators. Quartz has a natural high quality factor "Q", which enables the crystal to maintain high accuracy and frequency stability over the entire operating temperature and voltage range.

　　Advantages: The signal level is variable, that is, it is determined by the oscillator circuit. The same crystal can be used for a variety of voltages and can be used for chips with different clock signal voltage requirements. The price is usually lower. The accuracy of the crystal resonator is 1PPM (one millionth) to 100PPM.

　　Disadvantages: The crystal resonator is a non-polar component with two pins. It needs the help of a clock circuit to generate an oscillation signal and cannot oscillate by itself. Compared with the crystal oscillator, the defect of the crystal resonator is that the signal quality is poor. Usually, it needs to accurately match the peripheral circuit (capacitors, inductors, resistors, etc. for signal matching). When replacing crystals of different frequencies, the peripheral configuration circuit needs to be adjusted accordingly.

　　Crystal resonators have some equivalent parameters, and different usage environments may have different requirements. When selecting, you must also consider the ambient temperature, load capacitance, frequency accuracy and other requirements. This requires that the parameters of the peripheral oscillation circuit be controlled in order to output a stable frequency.

　　Ceramic resonator

　　A ceramic resonator is a piezoelectric ceramic device that oscillates at a specific frequency. The material used to make this device has a resonant characteristic that is stimulated during the production process. Since this resonant characteristic is within the production tolerance range and its quality factor is much lower than that of quartz, the frequency stability that a ceramic resonator can provide is not as good as that of a crystal resonator. Ceramic resonators are usually used in applications where cost is low and performance requirements are not high.

　　Advantages: Compared to crystals, ceramic resonators cost only half as much and are smaller in size.

　　Disadvantages: Compared with crystals, it lacks frequency and temperature stability. Its accuracy is poor, about 1% to 0.1%.

　　Overview: Typical initial accuracy of ceramic resonators is in the 0.5% to 0.1% range, and drift due to aging or temperature changes may change this accuracy range. Inexpensive ceramic resonators have a tolerance of only ±1.1%, while higher-end automotive accuracies are ±0.25% and ±0.3%, respectively. Future applications are in automotive CAN (Controller Area Network) bus applications, operating temperature is -40°C to +125°C. Low-cost ceramic resonators with frequencies of 200 KHZ to about 1 GHZ are suitable for embedded systems where timing requirements are not strict. Ceramic devices start faster and are generally smaller than quartz devices. They are also more resistant to shock and vibration.

　　Comparison of all resonant components:

　　Crystal Oscillator

　　Crystal

　　Advantages: Crystal oscillator signal quality is good, relatively stable, and the connection method is relatively simple (mainly to do a good job of power supply filtering, usually using a PI filter network composed of a capacitor and an inductor, and a small resistor at the output end to filter the signal), no complex configuration circuit is required. For applications with sensitive timing requirements, the performance of crystal oscillators is relatively good.

　　Disadvantages: Compared with crystal resonators, the disadvantages of crystal oscillators are that their signal level is fixed, and it is necessary to select the appropriate output level, which is less flexible and more expensive. In addition, quartz oscillators take a long time to start up.

　　Size: Crystal oscillators are usually larger than passive crystals. With the improvement of technology, some crystal oscillators are now surface-mounted and have a size comparable to that of crystal resonators.

　　Silicon Oscillator

　　Silicon oscillators, fully integrated oscillator components, are the simplest clock sources. These devices generate square waves of a specified frequency that can be fed directly into the clock input of a microcontroller. Silicon oscillators do not rely on mechanical resonance characteristics to obtain the oscillation frequency, but are based on an internal RC time constant. This design makes silicon devices insensitive to external mechanical effects. Unlike traditional oscillators, there are no exposed high-impedance nodes, which allows silicon oscillators to withstand greater humidity and EMI effects. Silicon oscillators do not require strictly matched timing components and circuit board traces.