Vice-versa, an electric stimulation in the same material will generate mechanical movements.
When a piezoelectric material is mechanically stimulated, it produces an electric signal. The functionality of crystal oscillators is thanks to the piezoelectric effect and the resulting inverse piezoelectric effect.
Crystals can do much, much better, as we’ll see shortly. LC oscillators fare a bit better, around 0.01%. RC oscillators with well-selected components can have a stability of 0.1%.
Atomic word clock series#
A varactor can be transformed into an excellent voltage-to-capacitance converter by placing a capacitor in series with it to eliminate the DC reverse bias current. Specially designed diodes, called varactors, are tuned to cover up to a 15:1 ratio in capacitance. The trick is to use a reversely-polarised diode junction exhibiting a voltage-dependent reverse-bias capacitance. Early radios used variable inductors or variable capacitors, but if your goal is to tweak the frequency electronically, the only practical way is to change the ‘C’ in LC. The most common types of LC oscillators are Colpitts and Hartley. They consist of some sort of LC network connected to an amplifier, with the amplifier providing positive feedback. LC resonators used to be the most widely adopted kind of oscillators when the world ran on wireless radios that were under a few hundred megahertz. If you so desire, you could use a pendulum as your next clock source, but for this article, we’ll limit the scope to resonators widely used in the electronic industry to generate a clock signal. Resonators can resonate due to their electrical properties (for example, LC resonators), electromechanical properties (for example, ceramics, crystals, and MEMS), electromagnetic wave propagation, or even atomic properties for atomic clocks.Īlmost everything can be a resonator, from skyscrapers to your lung cavity. When considering relaxation and delay sources, the higher their nominal frequency is, the more impractical the design becomes.Ī resonator is a device or system that exhibits resonant behaviour, oscillating with higher amplitude at some frequencies.In many kinds of resonators, these frequencies tend to be relatively narrow and stable, making them excellent oscillators. Often times, NOT ports connected in series are so unstable that you can use the frequency fluctuations of the oscillator as a true random number generator. You can obtain the same effect with any device that provides an adequate delay in the signal, for example, a bunch of NOT ports in series or a spool of wire that’s long enough to do the job.ĭelay oscillators usually have inferior stability when compared to other types of oscillators, so much so that semiconductor manufacturers use them to test wafers, as their performance is heavily temperature dependent. A series of RC elements can shift the phase of a signal to the necessary 180-degrees shift to achieve oscillation. The requirement to get an analogue circuit to oscillate is a 180-degrees phase shift at unity gain in a feedback loop. Parameters for this type of oscillator can be found below.
Instead, they produce sawtooth signals and square waves.Ī typical example of the RC relaxation oscillator is the famous NE555. Relaxation oscillators do not produce sinusoidal signals. The circuit oscillates between the charging and the discharging state. The capacitor is charged up to a defined voltage level, then the state of the device changes and the capacitor is discharged.
Relaxation oscillators are made of a switching device (usually BJTs, JFETs, Mosfets, or digital gates) and a capacitor to store charge. Let’s get started! Relaxation and Delay Sources RC Relaxation We’ll discuss the pros and cons of each clock source, from the RC in a 555-powered oscillator, to a Hydrogen Maser atomic clock. Luckily for us, such tradeoffs are relatively simple and can be explained almost fully within this single article. All clock sources present a series of tradeoffs regarding stability, reliability, size, power consumption and cost. In almost modern circuits, especially whenever digital circuitry is involved, you will find some kind of clock source.
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