The electrical equivalent circuit of the quartz crystal used in the vcxo is shown in figure 2. Using the 16 mhz crystal oscillator application note, rev. Used to analyse its response and predict its performance as. Hence, quartz crystal oscillator circuits are superior compared to other resonators such as lc circuits, turning forks, and so on. The quartz is most commonly used material for the crystal design. Here normal crystal oscillator symbol and its equivalent circuit given. A quartz crystals electrical equivalent model is that of a series tuned circuit in parallel with a capacitor, giving it some of the properties of both a parallel and a series tuned circuit. Basics of a quartz crystal microbalance introduction. There are certain parameters of a quartz crystal that need to match the parameters of the oscillator circuit for the best frequency accuracy and most reliable operation. In an electrical circuit, it is the number of times a resonator plate oscillates or vibrates in one second. A quartz crystal can be modelled using an equivalent circuit as shown on the right hand side. This chapter covers the electrical characteristics of quartz crystals from a. Tuning fork crystal electrical parameters the electrical parameters of a quartz crystal depending on its properties based on the quartz cut used.
Crystal equivalent circuit piezo electric crystals. Interestingly enough, we can write an equivalent electrical circuit to represent the mechanical properties of the crystal. You will be given an insight on resonance frequency measurements and impedance calculations. Simple electrical model of a fundamentalmode quartz crystal. The metalized surfaces are made for electrical connections, and the quartz physical size and density also the thickness is tightly. Crystal oscillators can be modelled as a series rlc circuit along with a parallel capacitor as shown in figure 1. Crystal symbol and its single mode, 1port, crystal resonator equivalent circuit in figure 1, c1, l1 and r1 form. The equivalent circuit of a crystal is shown in figure 8. Series resonant crystals are intended for use in circuits which contain no reactive components. The main parameters can be explained by the equivalent electrical circuit that is abstracted from a mechanical vibration model. The crystal equivalent circuit of the quartz crystal consists of a motional capacitance c1, the motional inductance. Crystal equivalent circuit the output frequency of oscillator circuits is normally not as stable as required for a great many applications. From a parallel circuit perspective, the overall electrical impedance of the crystal will be inversely proportional to the electrode area, as a larger electrode area is equivalent to multiple smaller electrode.
Quartz crystals, cut into thin plates and with electrodes plated on to opposite flat faces, can be used as resonant circuits with q values ranging from 20 000 to 1 000 000 or more. This equivalent circuit is can then be used to analyse its response and predict its performance as in the diagram below. A quartz crystal unit is a quartz wafer to which electrodes have been applied, and which is hermetically sealed in a holder structure. Mx processors is known as the colpitts oscillator with translated ground, illustrated in figure 1. The equivalent circuit contains series lcr circuits that represent resonant modes of the xtal. As can be shown these combinations occur at odd multiples odd overtones of the crystal of the fundamental series resonant frequency. The equivalent impedance of the crystal has a series resonance where cs resonates with inductance, ls at the crystals operating frequency. Generally, 8mhz crystal oscillator is used in microprocessors and microcontrollers. The crystal can be described by the electrical equivalent circuit in figure 2. When an electric field is placed upon it, a physical displacement occurs.
In this post let us discuss about the basics of crystal, how it works in electronics circuit. Figure 1 shows the electrical equivalent circuit of the crystal resonator. The component values all have tolerances, so that the actual oscillating frequency may easily be 10% higher or lower than the desired frequency. Figure 6 equivalent circuit the equivalent circuit, shown in figure 7, is an electrical depiction of the quartz crystal unit when operating at a frequency of natural resonance.
If a load capacitor cl is used in the application circuit it is in series with the crystal. The quartz crystal is made from thin piece of quartz wafer tightly fitted and controlled between two parallel metalized surfaces. Fundamentals of quartz oscillators application note 2002 h. Crystal oscillator circuits revised edition robert j. Quartz is a device that carries the piezoelectric characteris tics. The equivalent circuit, shown in figure b is an electrical depiction of the quartz crystal unit when operating at frequency of natural resonance. Hence, quartz crystal oscillator circuits are more superior compared to other resonators like lc circuits, tuning forks. Design a crystal oscillator to match your application.
A crystal with zero 0 load capacitance number has its reso nate frequency designated as fr, series resonant frequency. Generally in microprocessors and micro controllers we are using an 8mhz crystal oscillator. Equivalent circuit determination of quartz crystals. Equivalent electrical model the equivalent impedance of the crystal has a series resonance where cs resonates with inductance, ls at the. The mechanical vibration model and its electrical equivalent circuit. It has one resonant it and one antiresonant fa frequency. Rs ls cs co with known values of l s, c s, c 0 and r.
Understanding the quartz crystal resonator hackaday. Introduction to quartz frequency standards crystal unit equivalent circuit. Two parallel surfaces have metal plates bonded to or deposited onto them for connection to the electrical circuit. Circuit symbol for a quartz crystal resonator, xtal piezo electric effect. Measurement of the equivalent circuit of a quartz crystal. The electric equivalent circuit of a crystal cs is the motional capacitance. C1 and l1 represent the motion of the crystal as it vibrates.
Overview of crystal oscillator circuit working with. The equivalent diagram of quartz crystal involves a series rlc circuit due to the piezoelectric effect. Reactance in series, in parallel, or a combination of reactances can impact the electrical crystal substitute model by influencing its resonant oscillation frequency. When connected into an amplifier circuit, figure 2, a small amount of energy is fed back. Here equivalent circuit contains two segments one is to represent friction and stiffness of quartz crystal and another one is to. The equivalent circuit of a crystal unit is the series combination of the motional equivalents of inductance l1, capacitance c1 and resistance r1 and in parallel with this string the package and parasitic capacitance c0. What are piezoelectric characteristics of a quartz crystal unit. Making electrical contact to a quartz crystal is most easily done be addition of an electrode to each face of the crystal.
How a quartz crystal resonator works electronics notes. Crystal resonator c 0 l 1 c 1 r 1 r 2 r 3 l 2 c 2 t l 3 c 3 quartz quartz crystal is a piezoelectric material. Quartz crystals and micrel ics microchip technology. The equivalent circuit, shown in figure 7, is an electrical depiction of the quartz crystal unit. Quartz crystal glossary of terms nominal frequency. In order to analyze the quartz crystal oscillator, we must first understand the crystal itself. The crystal can be represented as the rlc circuit in the electrical equivalent circuit. Mechanical and electrical characteristics of a quartz crystal in an oscillator circuit are a. The usage and applications for quartz crystal devices is increas.
This is possible since the crystal acts like a tuned circuit when placed in an amplifier feedback arrangement. Piezoelectric transducer circuit, working and applications. Vibrations at higher multiples of the fundamental frequency are called overtones. An equivalent description of a quartz crystal is given by the following circuit. These series parallel resonance combination occurs at odd multiples of the fundamental series resonance frequency. Crystal oscillator diy electrical electronics projects. Analysis of change in motional capacitance of electrical equivalent circuit of quartzcrystal tuningfork tactile sensor induced by viscoelastic materials in contact with its base hideaki itoh and naoki hatakeyama faculty of engineering, shinshu university, nagano 3808553, japan email. Crystal equivalent circuit, motional parameters, and.
This capacitance is called as mounting capacitance cm which exists between two metal plates separated by a dielectric as crystal slab. It describes measurement methods and techniques in which a generator of continuously adjustable frequency of stability comparable to that of a crystal unit permits the use of such laboratory instruments as rf bridges and qmeters to. The losses associated with quartz crystals are very low and this means that the selectivity or q quality factor is exceedingly high. As we know the quartz crystal converts one type of energy into another energy hence it called as transducer. Introduction to quartz frequency standards crystal unit. Using the 16 mhz crystal oscillator nxp semiconductors. Short tutorial on quartz crystals and oscillators geyer electronic. Notes in the first circuit, above the bc548 is wired as a colpitts oscillator, the frequency tuned by insertion of a crystal. C1, l1 and r1 are called the motional parameters of the crystal, and c0 is the shunt capacitance.
Equivalent circuit model for a quartz crystal immersed in a liquid. The mechanical oscillation, piezo electrically excited by an alternating electrical field of suitable frequency, corresponds. Quartz crystal oscillators tend to operate towards their series resonance. The equivalent electrical circuit for a quartz crystal at its fundamental frequency the lowest at which it has a natural resonance is shown in figure 3b.
A good crystal will create high frequency oscillations, the output at the collector is rectified by the germanium oa91 diode and a deflection will appear on the meter. The equivalent electrical circuit also represents the crystal action of the crystal. The geometry of this crystal determines the fundamental or characteristic frequency. Analysis of change in motional capacitance of electrical. Matthys 05k krieger publishing company malabar, florida. Precision measurement electrical characteristics quartz. The equivalent electrical circuit for the quartz crystal shows a series rlc circuit, which represents the mechanical vibrations of the crystal, in parallel with a.
The wafer is often referred to as the blank, or the crystal plate. The amount of frequency deviation from the ambient temperature frequency over the operating temperature. The co, or shunt capacitance, represents the capacitance of the crystal electrodes. It is valid in the region of a single seriesparallel resonance combination. What do you think is the reason quartz is used so often. When looking at how a quartz crystal works, it is first necessary to understand the basics of the piezo electric effect.
The crystal by itself acts as a series resonant circuit with a very large inductance, small capacitance and fairly low resistance a few thousand ohms. Many micrel timing ics use a quartz crystal for the frequency reference. It represents the piezoelectric charge gained from a displacement in the crystal. Finite element prediction of q and equivalent electrical. The equivalent electrical circuit for the quartz crystal shows a series rlc circuit, which represents the mechanical vibrations of the crystal, in parallel with a capacitance, cp which represents the electrical connections to the crystal. To analyse the electrical response of a quartz crystal resonator, it is very often useful to depict it as the equivalent electrical components that would be needed to replace it. This application note describes how to measure the equivalent circuit parameters of a quartz crystal with the sark110 antenna analyzer. Quartz crystal oscillator and quartz crystals electronicstutorials. Request pdf finite element prediction of q and equivalent electrical parameters of quartz resonators the equivalent electrical parameters c0, c1, l1 and r1 can be calculated in an eigenvalue.
The equivalent circuit of a normal crystal is shown in figure 1, a. Equivalent circuit for a quartz crystal near fundamental resonance. The co, or shunt capacitance, represents the capacitance of the crystal electrodes plus the capacitance, of the holder leads. The electrical equivalent circuit of a quartz crystal unit consists of a series branch of a capacitor c1, a inductor l1. Electrical characteristics of quartzcrystal units and their. Equivalent circuit determination of quartz crystals sark. When connected into an amplifier circuit, figure 2, a small amount of energy is fed back to the crystal which causes it to vibrate. The process for the determination of the crystal parameters is laborious, so in order to simplify this process the sark110 provides the automatic determination of the crystal parameters feature.
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