In the field of electronic engineering, crystals (crystal oscillators) are one of the key components that ensure the stable operation of electronic devices. They utilize the inherent frequency characteristics of the crystal material to generate a stable clock signal, providing a time reference for the system. Crystals are divided into two main categories: active crystals and passive crystals. Although both are used to generate clock signals, but they are in the structure, principle of operation, performance and application scenarios there are significant differences.

I. The pin and structure differences

First of all, from the physical structure, passive crystal oscillator usually only two pins, is a kind of non-polar components. This simple structure means that it can not directly generate its own oscillating signal, but need to use the external clock circuit to stimulate oscillation. At the heart of a passive crystal is a resonant device based on a quartz crystal, which, when excited by a current, utilizes the quartz crystal's natural electro-mechanical effect to produce a precise frequency.

In contrast, active crystals have a more complex structure and typically contain four pins for power, ground, signal output, and null (NC). Active crystals not only contain quartz crystals, but also integrate peripheral circuits such as transistors and resistive elements to form a complete oscillator. This integrated design allows the active crystal oscillator to directly output a stable square wave or sine wave signal without relying on external clock circuits.

II. The principle of operation and performance comparison

In the principle of operation, passive crystal needs to rely on the energy provided by external circuits to stimulate oscillation, its signal level is variable, depending on the design of the starting circuit. Since passive crystal does not have a built-in amplification circuit, its output signal power is relatively low and may require further amplification or processing before it can be supplied to other devices. In addition, the accuracy of passive crystals is usually around 5 ppm, which is sufficient for many general applications, but may not be sufficient for high-precision applications with sensitive timing requirements.

In contrast, active crystals utilize the piezoelectric effect of quartz crystals and compensate for the energy loss of the crystal oscillator through internal amplification circuits to maintain stable oscillation. This design not only improves signal stability and accuracy (up to 0.1ppm), but also simplifies the connection with external circuits. Active crystal oscillator can directly output higher power and amplitude signal, can directly drive other circuits, without additional amplification or processing.

III. Application scenarios and cost considerations

Because passive crystals are simple, low cost and easy to integrate into various circuits, they are widely used in a variety of consumer electronics products, such as cell phones, tablet PCs and TVs. In these applications, the accuracy and stability of passive crystals are usually sufficient to meet system requirements without significantly affecting overall performance.

However, active crystals are preferred in applications that require high accuracy and stability of the clock signal, such as communications equipment, computer servers and precision measuring instruments. These applications have extremely stringent timing requirements, and any small clock deviation can lead to system performance degradation or failure. Therefore, despite the relatively high cost of active crystals, their excellent performance and stability make them indispensable in these areas.

In addition, active crystals are relatively simple to connect and usually only require good power supply filtering (usually using a PI-type filtering network consisting of a capacitor and an inductor, with a small resistance resistor at the output to filter the signal). This simple configuration reduces the complexity of the system design, and improves the reliability and stability of the system.

IV. Flexibility and adaptability

In terms of flexibility, passive crystals have a greater advantage. Because they do not have a fixed signal level, so can be applied to a variety of voltage and clock signal voltage requirements of the DSP (digital signal processor). This flexibility allows passive crystals to find application in many different electronic devices and systems.

However, the signal level of an active crystal is fixed, so special attention needs to be paid to matching the output level to the receiving circuit when selecting one. If the output level is too high or too low, it may result in signal distortion or failure to properly drive the receiving circuit. Therefore, when using active crystal oscillator, you need to carefully select and configure according to the specific application scenarios and needs.

V. Summary

In summary, there are significant differences between active and passive crystals in terms of pinout and structure, operating principle and performance, application scenarios and cost, as well as flexibility and adaptability. These differences make the two have their own unique advantages and scope of application in the field of electronic engineering. When selecting a crystal, comprehensive consideration needs to be made based on specific application scenarios and requirements to ensure system stability and performance. Through an in-depth understanding of the differences between active and passive crystals, we can better select the appropriate clock source for electronic equipment, thereby promoting the continued development and progress of electronic technology.