How does quartz oscillator circuit work | Xtalong
Quartz Crystal Oscillator (Quartz Crystal Oscillator) is abbreviated as Active Crystal Oscillator, or OSC in English. It can generate the clock frequency signal necessary for the central processing unit (CPU) to execute instructions. The execution of all instructions of the CPU is based on this foundation. above. Generally speaking, the higher the frequency of the clock signal, the faster the CPU runs and the higher the efficiency of data processing.
At present, most intelligent digital electronic products have at least one clock source. In other words, even if the oscillator circuit cannot be seen with the eyes on some circuit boards, there will be an integrated clock signal inside the chip. The clock signal is called The heart of digital circuitry.
The working principle of the oscillating circuit is: after the standard voltage is input from the outside, the active crystal oscillator can output a nominal periodic clock signal, that is, the nominal frequency (Normal Frequency), which is the frequency specified in the crystal oscillator specification, and is also the frequency specified by the engineer in the crystal oscillator specification. The important electrical parameters of the crystal oscillator that are of primary concern in circuit design and crystal oscillator procurement. The nominal frequency of common MHz crystal oscillators is between 1 and 200MHz, such as 2.048MHz, 4MHz, 8MHz, 11.0592MHz, 12MHz, 24MHz, 25MHz, 26MHz, 27MHz, 54MHz, 125MHz, etc. PLL (lock The principle of phase loop) multiplies the low frequency to more than 1GHz. The most common KHz crystal oscillator is 32.768KHz crystal oscillator, which is mainly used to realize the time display function, so it is often called a watch crystal by us.
In the practical application of the crystal oscillator, there will inevitably be a certain deviation in the signal frequency output by the crystal oscillator during work. At this time, we often encounter two words to describe this error phenomenon of the crystal oscillator: frequency tolerance or Frequency Stability, expressed in units of PPM, that is, Parts Per Million: 1/1000000, which refers to the relative frequency of the crystal oscillator in operation within a specified temperature range. The smaller the PPM value, the higher the precision of the crystal oscillator. For example, the deviation of the 12MHz crystal oscillator is ±20ppm, which means that its frequency deviation is 12×20Hz=±240Hz, that is, the frequency range is (11.999760～12.000240Hz).
In addition, there is another technical term that needs to be explained, that is, Frequency Stability vs Temperature, which indicates the allowable deviation of the operating frequency from the reference temperature (25°C) within a specific temperature range, and its unit is also PPM . Similarly, the smaller the PPM, the smaller the temperature drift of the crystal oscillator, that is, the higher the stability. Then, of course, it is impossible for electronic equipment to work under the ideal condition that the temperature environment is 25°C all the time. What if it is in other temperature ranges? Therefore, if some electronic products need to work under the condition of large temperature difference outdoors, it is necessary to consider the degree of frequency deviation of the crystal oscillator in different temperature ranges, for example: temperature frequency difference: ±15ppm~±30ppm, operating temperature range: -20 °C ~+70°C; Temperature frequency difference: ±15ppm~±30ppm, working temperature range -40°C ~+85°C.
We often notice other parameters, such as load capacitance, resonance resistance, static capacitance, etc., which are related to the physical characteristics and production process of the crystal oscillator.
It is also important to point out that the quartz crystal resonator, that is, the passive crystal oscillator, cannot generate an oscillation signal by itself, and must be realized by means of a matching external oscillator circuit. The application of active crystal oscillator is much simpler. If you need any output frequency, just purchase the active crystal oscillator (OSC) of this frequency, which saves a lot of precious time by eliminating the complicated matching process of using formula calculations and manually repeatedly welding external capacitors. At the same time, the active crystal oscillator also avoids the interference of stray capacitance to a large extent, and its performance is more stable. Some people may think that the price of the active crystal oscillator is more expensive than the passive crystal oscillator, but the active crystal oscillator has a built-in IC, and the circuit board will naturally save an IC, so in general, the cost of the circuit board is not. Increase.
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