What is a crystal oscillator (crystal oscillator)?

Some electronic devices require an AC signal with a highly stable frequency, while the LC oscillator has poor stability and unstable frequency (the frequency of the generated AC signal is easy to change). A special component is used in the oscillator, a quartz crystal, which can generate a highly stable signal. This oscillator using a quartz crystal is called a crystal oscillator (crystal oscillator).

Classification of crystal oscillators
There are several categories of crystal oscillators: series crystal oscillators, parallel crystal oscillators, temperature-compensated crystal oscillators, non-temperature-compensated crystal oscillators, and voltage-controlled crystal oscillators. However, active crystal oscillators and passive crystal oscillators do not have positive and negative feedback polarity conditions, and can only be used as one-way guidance, and do not belong to the classification of series and parallel crystal oscillators. In the application of the semiconductor industry, the crystal oscillator can be regarded as the absolute only position, and the quartz crystal oscillator is required to stabilize the signal frequency in electronic components or electronic equipment.

The passive crystal oscillator is a non-polar component with only 2 pins. The passive crystal oscillator cannot generate oscillation by itself, and it needs the help of a clock circuit to generate an oscillation signal. The passive crystal oscillator does not have the problem of load voltage, its signal level can be changed, that is to say, its signal dependence is determined according to the clock circuit, so the passive crystal oscillator can be applied to a variety of voltages for different clock signals DSP with high voltage requirements, and the price is relatively low, especially suitable for producers with rich product lines and large batches.

However, the defects of passive crystal oscillators are also very obvious. The signal quality of passive crystal oscillators is poor and must rely on accurate peripheral circuit matching. When replacing crystals with different frequencies, the surrounding circuit configuration must also be modified and adjusted. Cumbersome and exhausting.

Active crystal oscillator has 4 pins, compared to passive crystal oscillator, it is a complete crystal oscillator. The active crystal oscillator does not need to use peripheral circuits to oscillate, its signal quality is very good and stable, and the connection method is relatively simple (mainly for power supply filtering, usually using a PI filter network composed of capacitors and inductors) , the output end can filter the signal with a small resistance resistance), it does not need to configure a very complicated circuit, it is one of the crystal oscillators that semiconductor companies are very fond of nowadays. Compared with passive crystals, active crystal oscillators have the defect of fixed signal level, and must have a suitable fixed signal level to output, so relatively speaking, the flexibility is not high and the cost will increase.

However, for applications that are sensitive to timing requirements, an active crystal oscillator is better. Adding an active crystal oscillator to the wireless transparent transmission module application improves the timeliness of data transparent transmission and makes the user's needs more convenient, efficient and faster.

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