Behind Precise Clock Signals: Active & Passive Crystals' Principles and Applications

The active crystal oscillator with an internal oscillation circuit has the advantage of independent startup, getting rid of the dependence on external capacitors and being able to start directly and work independently without the support of external capacitors. In principle, the active crystal oscillator can work immediately after the power supply is connected; relatively speaking, the performance of the passive crystal depends on precise capacitance matching. Choosing the appropriate capacitor is the key to the startup and operation of the crystal oscillator and plays a crucial role in the stability and performance of the entire system. We can ensure the efficient startup and stable operation of the crystal oscillator. Nevertheless, if this key component is not equipped, the crystal oscillator performance will not reach the oscillation level corresponding to its specification.

Passive Crystal Oscillator (PCO)

According to the instructions in the product manual, the activation of the passive crystal depends on the oscillator integrated in the DSP chip, and the detailed process of its connection and configuration is elaborated in the manual. Because the passive crystal does not depend on voltage and can adapt to the characteristics of the oscillation starting circuit, the same crystal can adapt to multiple voltage environments. This feature makes passive crystals suitable for DSP clock signal sources with various voltage requirements. Passive crystals are not only relatively economical in price but also particularly suitable for enterprises with rich product lines and large production volumes due to their versatility. If conditions permit, in conventional applications, passive crystals are recommended as the first choice.

When designing the peripheral circuit of the passive crystal, it must be considered that its signal quality may not fully meet expectations, which requires more refined circuit matching. Precise calibration of the peripheral circuit becomes a necessary operation after the frequency update of the crystal element to match the new frequency characteristics. When comparing and analyzing with the performance of the crystal oscillator, especially when setting key components such as capacitors, inductors, and resistors, the importance of calibration is particularly prominent. If the precision requirement is high, high-precision quartz crystals should be preferred rather than ceramic crystals.

Active Crystal Oscillator (ACO)

When compared with the oscillator built into the DSP chip, the active crystal oscillator is superior. The oscillation source independent of the chip gives it the unique ability to ensure the stability and accuracy of the clock signal. Its connection method is relatively easy, and the key lies in the filtering of the power supply. A common way to achieve this goal is to use a dual-capacitor filter, that is, a combination of a capacitor and an inductor. Finally, at the output stage, only a small resistance value resistor is required for signal purification, and no complex additional circuit design is required to meet the performance requirements.

In terms of signal level stability, the performance advantage of the active crystal oscillator is significant. In contrast, in applications with extremely high performance requirements, the level variability of the passive crystal may expose its performance deficiencies. The typical pin connection of the active crystal oscillator usually follows the following configuration: unconnected pin, ground pin, signal output pin, and power input pin. The appropriate output level must be determined during the design stage, which not only limits the flexibility of the application but also usually leads to an increase in cost.

In occasions where strict clock accuracy must be maintained, the active crystal oscillator becomes the first choice because it provides a highly stable oscillation solution including temperature compensation to ensure that the clock accuracy reaches the highest standard. In addition, some DSPs, such as the 6000 series of TI, must be used with active crystal oscillators due to the lack of a built-in oscillation starting circuit. Although active crystal oscillators are traditionally large in size, many contemporary products use surface mount technology, making their size comparable to that of passive crystals, and some products even achieve a more compact design.

About Mandu Technology

Shenzhen Mandu Technology Co., Ltd. has steadfastly centered its operations on the distribution of high-performance, high-quality, and highly reliable integrated circuit products. Its portfolio encompasses memory chips, differential crystal oscillators, and MCU microcontrollers, while progressively integrating analog signal chain products. The company prides itself on delivering comprehensive and cost-effective solutions to its customers. Its products find applications across a broad spectrum of industries, including but not limited to network communication, industrial control, robotics, medical equipment, personal health, and numerous other fields.

Business: sales@manduic.com

Website: www.manduic.com

Sales: +86 150-1290-5940

#Keywords: Mandu Technology, PUYA, ISSI, Epson, Hongxing, NOR FLASH, FLASH, Crystal Oscillator