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