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A crystal oscillator is a component in a circuit that can provide a highly stable clock signal. Usually, a system shares a crystal oscillator to facilitate synchronization of various parts and "do great things" together. For example, in our commonly used computer systems, the crystal oscillator can be likened to the "heartbeat" generator of each board. If there is a problem with the "heartbeat" of the main card, other circuits will inevitably fail. The human heartbeat is inseparable from blood. The same is true for crystal oscillators, which are inseparable from current.
Simply put, the driving force of the crystal oscillator is electricity. We need to put a crystal oscillator in a complete circuit and power the circuit to generate a loop current. From then on, the crystal oscillator begins to "beat" stably and rhythmically.
Of course, this oscillator circuit is also particular (active crystal oscillators have built-in oscillator circuits, and passive crystal oscillators require external oscillator circuits), and it needs to follow the "Barkhausen stability criterion".
Crystal oscillators provide clock signals in traffic light systems
· What is the Barkhausen stability criterion?
The Barkhausen stability criterion, a criterion proposed by German physicist Heinrich Georg Barkhausen in 1921, states that the phase difference of the electronic oscillator system signal from input to output and then back to input is 360°, and the loop gain is ≥1, which is a necessary condition for the oscillator to start.
A simple oscillator wants to produce periodic oscillations, usually in the form of voltage output. While continuously outputting, it needs to add an amplifier to generate continuous feedback to the input. Since the output of the amplifier itself has too large a phase shift at high frequencies, the entire feedback will become positive, thus generating oscillations.
When the loop gain is ≥1, it means that the input signal is sent to the input end after a circle in the loop, and the signal amplitude is larger than before. The phase is 360°, which means that after the input signal has traveled around the circuit, the phase is exactly the same as the original input signal, so the input signal is perfectly enhanced.
Combining the two, the signal increases after repeated amplification. When the signal amplitude in the loop increases to a certain extent, the nonlinearity of the active device in the oscillator (the inverter in the crystal oscillator circuit) will limit the further increase of the amplitude, making the output of the oscillator stable. In layman's terms, the amplitude of the oscillation will definitely not exceed the power supply voltage.
