What Are the Differences Between an Oscillator and a Resonator?

1. Oscillator

An oscillator is a device that converts DC power into AC power with a specific frequency. The circuit formed by this device is known as an oscillator circuit. As an active electronic component, the oscillator includes a control circuit in addition to the resonator. Oscillators are used to generate repetitive electronic signals, typically in the form of sine waves or square waves. These devices convert direct current into alternating current signals at a defined frequency.

There are various types of oscillators, classified based on different criteria:

- Excitation Mode: Self-excited oscillators and separately excited oscillators.

- Circuit Structure: Resistance-capacitance (RC) oscillators, inductance-capacitance (LC) oscillators, crystal oscillators, and tuning fork oscillators.

- Output Waveform: Sine wave, square wave, sawtooth wave, and other types of oscillators.

Oscillators are widely used in the electronics industry, medical devices, scientific research, and many other fields.

1.1 Crystal Oscillator

Advantages: Crystal oscillators provide high signal quality with good stability. The connection process is relatively straightforward, primarily requiring effective power filtering. Typically, a PI-type filter network, consisting of capacitors and inductors, is used, along with a small resistance resistor to filter the output signal. No complex circuitry is needed. Crystal oscillators perform well in applications with sensitive timing requirements.

Disadvantages: Unlike crystal resonators, crystal oscillators have a fixed signal level, requiring careful selection of the appropriate output level. This limits flexibility and increases the cost. Additionally, quartz oscillators have a longer startup time.

Size: Compared to passive crystals, crystal oscillators are generally larger in size. However, with technological advancements, some crystal oscillators are now available in surface-mount form, with sizes comparable to those of crystal resonators.

1.2 Silicon Oscillator

A silicon oscillator is a fully integrated component that serves as a simple clock source. It generates a square wave with a specified frequency, which can be directly input into the microcontroller's clock. Unlike traditional oscillators, the silicon oscillator does not rely on mechanical resonance for its oscillation frequency. Instead, it uses an internal RC time constant. This design makes silicon oscillators resistant to external mechanical influences. Additionally, they do not have exposed high-impedance nodes, making them more resilient to humidity and electromagnetic interference (EMI). Silicon oscillators also eliminate the need for precisely matched timing components and circuit board traces.

2. Resonator

A resonator is an electronic component that generates a resonant frequency. As a typical passive device, it requires a peripheral circuit to operate and produce a clock output. Resonators are commonly classified into two types: quartz crystal resonators and ceramic resonators. These components are known for their stability and excellent anti-interference performance, making them widely used in various electronic products. Quartz crystal resonators offer higher frequency accuracy compared to ceramic resonators but come at a higher cost. The primary function of a resonator is frequency control, and it plays an essential role in any electronic device that involves frequency transmission and reception. Resonators are available in two main forms: in-line and surface-mount (patch) types.

2.1 Quartz Crystal Resonator

Quartz crystal, commonly referred to as crystal, is composed of SiO2 and is a vital piezoelectric material. Its key characteristic is the regular arrangement of atoms or molecules, which is reflected in its macroscopic symmetry. When exposed to an electric field, internal stress and deformation occur within the crystal, generating mechanical vibrations at a specific frequency. This vibration, along with the crystal's inverse piezoelectric effect, is utilized to create a quartz crystal resonator. Quartz crystals have a naturally high-quality factor (Q), which allows them to maintain exceptional frequency accuracy and stability across a wide range of operating temperatures and voltages.

Advantages: The signal level of a crystal resonator is variable, meaning it is determined by the oscillating circuit. The same crystal can be used across various voltages and is compatible with different chips requiring different clock signal voltages. Additionally, crystal resonators are typically more affordable. Their frequency accuracy ranges from 1 PPM (parts per million) to 100 PPM.

Disadvantages: A crystal resonator is a non-polar component with two pins, and it requires a clock circuit to generate an oscillating signal—it cannot oscillate on its own. In comparison to crystal oscillators, crystal resonators tend to have lower signal quality and often need precise matching with peripheral circuits (such as capacitors, inductors, and resistors) for optimal signal performance. When changing crystals with different frequencies, the peripheral circuit configuration must be adjusted accordingly.

Crystal resonators have equivalent parameters that may vary depending on the usage environment. When selecting a resonator, factors like operating temperature, load capacitance, and frequency accuracy must be considered. This requires careful control of the parameters in the peripheral oscillator circuit to ensure stable frequency output.

2.2 Ceramic Resonator

A ceramic resonator is a piezoelectric ceramic device designed to oscillate at a specific frequency. The materials used in its construction excite resonance characteristics during manufacturing. However, due to production tolerances and a lower quality factor compared to quartz, ceramic resonators offer less frequency stability. As a result, they are generally used in applications where cost is a primary concern and performance requirements are not as stringent.

Advantages: Ceramic resonators are significantly more affordable than crystal resonators, typically costing only half as much, and they are smaller in size.

Disadvantages: Ceramic resonators have lower frequency and temperature stability compared to crystals. Their accuracy is also poorer, ranging from 1% to 0.1%.

Summary: The typical initial accuracy of ceramic resonators is between 0.5% and 0.1%, though this may vary due to aging or temperature fluctuations. Low-cost ceramic resonators may have tolerances as wide as ±1.1%, while higher-end models, such as those used in automotive applications, can achieve accuracies of ±0.25% to ±0.3%. Ceramic resonators are commonly used in automotive CAN (Controller Area Network) bus applications, with an operating temperature range of -40°C to +125°C. These resonators, which typically operate in frequencies ranging from 200 kHz to 1 GHz, are ideal for embedded systems with less demanding timing requirements. They start up faster, are smaller than quartz resonators, and are more resilient to shock and vibration.

3. Main Applications of Oscillators and Resonators

An oscillator is a device that converts DC electrical energy into AC electrical energy to generate AC signals at a specific frequency. It is an active component. In contrast, a resonator is a circuit that resonates at a particular frequency, primarily used to filter out specific frequencies. It is a passive component. A crystal resonator, being passive, does not require a power supply. On the other hand, a crystal oscillator is an active device that requires a power source. The key component in a crystal oscillator circuit is the crystal resonator. The resonator is incorporated into an external oscillating circuit, amplification circuit, or filter circuit to form the complete crystal oscillator.