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. Finite element prediction of q and equivalent electrical. Introduction to quartz frequency standards crystal unit equivalent circuit. This is possible since the crystal acts like a tuned circuit when placed in an amplifier feedback arrangement. Here normal crystal oscillator symbol and its equivalent circuit given. The equivalent circuit, shown in figure b is an electrical depiction of the quartz crystal unit when operating at frequency of natural resonance. Precision measurement electrical characteristics quartz. 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. 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. 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. In this post let us discuss about the basics of crystal, how it works in electronics circuit. Mechanical and electrical characteristics of a quartz crystal in an oscillator circuit are a. Equivalent circuit model for a quartz crystal immersed in a liquid.
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. C1, l1 and r1 are called the motional parameters of the crystal, and c0 is the shunt capacitance. Generally in microprocessors and micro controllers we are using an 8mhz crystal oscillator. Tuning fork crystal electrical parameters the electrical parameters of a quartz crystal depending on its properties based on the quartz cut used. Mx processors is known as the colpitts oscillator with translated ground, illustrated in figure 1. Reactance in series, in parallel, or a combination of reactances can impact the electrical crystal substitute model by influencing its resonant oscillation frequency. Using the 16 mhz crystal oscillator nxp semiconductors. The electric equivalent circuit of a crystal cs is the motional capacitance. The co, or shunt capacitance, represents the capacitance of the crystal electrodes. 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 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. Crystal equivalent circuit piezo electric crystals.
The equivalent electrical circuit also represents the crystal action of the crystal. Quartz crystal glossary of terms nominal frequency. Making electrical contact to a quartz crystal is most easily done be addition of an electrode to each face of the crystal. The wafer is often referred to as the blank, or the crystal plate. A crystal with zero 0 load capacitance number has its reso nate frequency designated as fr, series resonant frequency. Equivalent electrical model the equivalent impedance of the crystal has a series resonance where cs resonates with inductance, ls at the. When looking at how a quartz crystal works, it is first necessary to understand the basics of the piezo electric effect.
The usage and applications for quartz crystal devices is increas. Measurement of the equivalent circuit of a quartz crystal. The equivalent diagram of quartz crystal involves a series rlc circuit due to the piezoelectric effect. This capacitance is called as mounting capacitance cm which exists between two metal plates separated by a dielectric as crystal slab. The main parameters can be explained by the equivalent electrical circuit that is abstracted from a mechanical vibration model. Two parallel surfaces have metal plates bonded to or deposited onto them for connection to the electrical circuit. In order to analyze the quartz crystal oscillator, we must first understand the crystal itself. Quartz crystals and micrel ics microchip technology. Quartz crystal oscillators tend to operate towards their series resonance. 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. Electrical characteristics of quartzcrystal units and their. 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. The quartz crystal is made from thin piece of quartz wafer tightly fitted and controlled between two parallel metalized surfaces.
The crystal can be described by the electrical equivalent circuit in figure 2. The metalized surfaces are made for electrical connections, and the quartz physical size and density also the thickness is tightly. Figure 1 shows the electrical equivalent circuit of the crystal resonator. Analysis of change in motional capacitance of electrical. Simple electrical model of a fundamentalmode quartz crystal. Crystal oscillator circuits revised edition robert j. Equivalent circuit determination of quartz crystals sark. It has one resonant it and one antiresonant fa frequency. The equivalent electrical circuit also describes the crystal action of the crystal. An equivalent description of a quartz crystal is given by the following circuit. 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 electrical equivalent circuit of the quartz crystal used in the vcxo is shown in figure 2. 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. It is valid in the region of a single seriesparallel resonance combination.
Here equivalent circuit contains two segments one is to represent friction and stiffness of quartz crystal and another one is to. 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. This equivalent circuit is can then be used to analyse its response and predict its performance as in the diagram below. Piezoelectric transducer circuit, working and applications. The component values all have tolerances, so that the actual oscillating frequency may easily be 10% higher or lower than the desired frequency. As can be shown these combinations occur at odd multiples odd overtones of the crystal of the fundamental series resonant frequency. 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. Quartz crystal oscillator and quartz crystals electronicstutorials. 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 impedance of the crystal has a series resonance where cs resonates with inductance, ls at the crystals operating frequency. Design a crystal oscillator to match your application. The equivalent circuit of a normal crystal is shown in figure 1, a. Hence, quartz crystal oscillator circuits are superior compared to other resonators such as lc circuits, turning forks, and so on. Overview of crystal oscillator circuit working with. This chapter covers the electrical characteristics of quartz crystals from a. Circuit symbol for a quartz crystal resonator, xtal piezo electric effect. Design guidelines for quartz crystal oscillators iqd frequency. The mechanical oscillation, piezo electrically excited by an alternating electrical field of suitable frequency, corresponds.
Quartz is a device that carries the piezoelectric characteris tics. Rs ls cs co with known values of l s, c s, c 0 and r. Interestingly enough, we can write an equivalent electrical circuit to represent the mechanical properties of the crystal. The amount of frequency deviation from the ambient temperature frequency over the operating temperature. A quartz crystal unit is a quartz wafer to which electrodes have been applied, and which is hermetically sealed in a holder structure. 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. Crystal oscillator diy electrical electronics projects. How a quartz crystal resonator works electronics notes. It represents the piezoelectric charge gained from a displacement in the crystal. Series resonant crystals are intended for use in circuits which contain no reactive components. 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. Introduction to quartz frequency standards crystal unit. This application note describes how to measure the equivalent circuit parameters of a quartz crystal with the sark110 antenna analyzer. The quartz is most commonly used material for the crystal design.
C1 and l1 represent the motion of the crystal as it vibrates. 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. 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. You will be given an insight on resonance frequency measurements and impedance calculations. Understanding the quartz crystal resonator hackaday. Crystal equivalent circuit the output frequency of oscillator circuits is normally not as stable as required for a great many applications. Equivalent circuit determination of quartz crystals. 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. The equivalent circuit contains series lcr circuits that represent resonant modes of the xtal.
The crystal can be represented as the rlc circuit in the electrical equivalent circuit. The electrical equivalent circuit of a quartz crystal unit consists of a series branch of a capacitor c1, a inductor l1. Using the 16 mhz crystal oscillator application note, rev. As we know the quartz crystal converts one type of energy into another energy hence it called as transducer. What do you think is the reason quartz is used so often. In an electrical circuit, it is the number of times a resonator plate oscillates or vibrates in one second. When connected into an amplifier circuit, figure 2, a small amount of energy is fed back. Fundamentals of quartz oscillators application note 2002 h. The geometry of this crystal determines the fundamental or characteristic frequency. Hence, quartz crystal oscillator circuits are more superior compared to other resonators like lc circuits, tuning forks. When an electric field is placed upon it, a physical displacement occurs. Short tutorial on quartz crystals and oscillators geyer electronic. 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. The crystal equivalent circuit of the quartz crystal consists of a motional capacitance c1, the motional inductance.
Equivalent circuit for a quartz crystal near fundamental resonance. Basics of a quartz crystal microbalance gamry instruments. The equivalent circuit of a crystal is shown in figure 8. Crystal symbol and its single mode, 1port, crystal resonator equivalent circuit in figure 1, c1, l1 and r1 form. 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. If a load capacitor cl is used in the application circuit it is in series with the crystal. Vibrations at higher multiples of the fundamental frequency are called overtones. Crystal oscillators can be modelled as a series rlc circuit along with a parallel capacitor as shown in figure 1. What are piezoelectric characteristics of a quartz crystal unit. Many micrel timing ics use a quartz crystal for the frequency reference. Matthys 05k krieger publishing company malabar, florida. Crystal equivalent circuit, motional parameters, and. Basics of a quartz crystal microbalance introduction.
This model is valid in the frequency region of a single series parallel resonance combination. 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. These series parallel resonance combination occurs at odd multiples of the fundamental series resonance frequency. 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. Notes in the first circuit, above the bc548 is wired as a colpitts oscillator, the frequency tuned by insertion of a crystal.
523 217 278 887 718 404 979 1411 1116 368 468 1162 1566 1272 492 760 48 1465 164 1299 1391 583 107 620 777 616 135 213 211 747 190