Kingtronics Blog

A quartz crystal resonator depends on the piezo-electric effect to work. This effect converts a mechanical stress in a crystal to a voltage and vice versa. In this way the piezo-electric effect converts the electrical impulses to mechanical stress which is subject to the very high Q mechanical resonances of the crystal, and this is in turn linked back into the electrical circuit.

The quartz crystal can vibrate in several different ways, and this means that it has several resonances, all on different frequencies. Fortunately the way in which the quartz crystal blank is cut from the original crystal itself can very significantly reduce this. In fact the angle of the faces relative to the original crystal axes determines many of its properties from the way it vibrates to its activity, Q, and its temperature co-efficient. There are three main ways in which a crystal can vibrate: longitudinal mode, low frequency face shear mode, and high frequency shear. A cut known as the AT cut used for most crystals used in traditional radio and electronics circuits uses the high frequency shear mode.

Vibrational modes of a quartz crystal resonator
(For the sake of clarity, the movements have been greatly exaggerated)

The equivalent series resistance is the resistive element (R1) of the quartz crystal equivalent circuit. (see Equivalent Circuit below) This resistance represents the equivalent impedance of the crystal at natural resonant frequency (series resonance) ESR is measured by a Crystal Impedance (CI) meter.

ESR values are generally stated as maximum values expressed in ohms. The ESR values vary with frequency, mode of operation, holder type, crystal plate size, electrode size, and mounting structure.

It is worth noting that the ESR value at a given frequency for an AT- strip crystal design is generally higher than that of the standard (round blank) design. This becomes more significant at lower frequencies. When transitioning from a series resonant through-hole HC-49/U type crystal to a smaller surface mount type utilizing an AT-strip crystal, some consideration may be given to the difference in the ESR values produced by different cuts.

The ESR becomes critical when resistance values reach a point were the oscillator circuit cannot adequately drive the crystal. Sluggish start-up or unwanted modes of operation may result.

Equivalent Circuit:

The equivalent circuit (shown in Figure A) depicts electrical activity of a quartz crystal unit operating at its natural resonant frequency. The shunt capacitance (Co), represents the capacitance of the crystal electrodes plus the capacitance of the holder and leads. R1, C1, and L1 compose the "motional arm" of the crystal, and are referred to as the motional parameters. The motional inductance (L1) represents the vibrating mass of the crystal unit. The motional capacitance (C1) represents the elasticity of the quartz, and the resistance (R1), represents bulk losses occurring within the quartz.

Quartz crystals used in filters and oscillators in electronic circuits are renowned for their performance, stability, frequency tolerance and their high Q. Yet they do change their frequency very slightly with time in a process known as ageing. Although the frequency variations are small by many standards, they are permanent and may have an effect in some applications where the frequency is of great importance. As a result manufacturing techniques take account of this to reduce the effects of ageing in these crystals as far as possible.

Ageing is caused by a number of interrelated factors. These include internal contamination, excessive drive level, surface change of the crystal, various thermal effects, wire fatigue and frictional wear. The level of ageing can be minimised in a number of ways. During manufacture they should be encapsulated in an inert gas environment, the ensuring should have a good seal so that other gases do not enter. Also the final stages of the preparation of the crystal blank must be prepared as finely as possible. Rather than lapping the blank to bring it to the right dimensions, chemical etching is used. In this way the minimum disruption is caused to the crystal lattice, and this reduces the ingress of contaminants over time that will cause ageing.

The design of the circuit in which the crystal will be used also has an effect. By keeping the drive levels low again the crystal ageing will be less.

The frequency of the quartz crystal is obviously a fundamental specification. It is normally expressed to as many significant figures as demanded by the frequency tolerance, although seven figures is normally the maximum. It is wise to express the frequency to the right number of significant figures to avoid misunderstandings in this area of the quartz crystal specification.

Kingtronica Quartz Crystal series are popular in the word market , Quartz Crystal include HC49U, HC49S and SMD quartz crystal HC49SMD .The HC49U is available in tight tolerances and stabilities for demanding applications. With a broad frequency range from 1.8432MHz to 200.000MHz, the HC49U can serve as a low cost solution in virtually any application or market.

The temperature stability is another important area of the crystal specification and it is the allowable frequency deviation as the temperature varies. Again normally expressed in ppm, from the frequency at the reference temperature per degree Celsius. Sometimes the crystal specification may use a frequency tolerance consisting of the sum of the calibration and temperature stability tolerances is quoted.

Over the Operating Temperature Range, an amount of total deviation acceptable for the application. Tighter specifications of Stability lower yield in Quartz Crystal Blank production thereby serving to increase production costs

Kingtronics offers high quality quartz crystal at incredibly aggressive prices. The HC49S series is an industry standard crystal package. HC49S is a low cost, low profile timing option for applications where cost is critical.

The HC49S is available in tight tolerances and stabilities for demanding applications. With a broad frequency range from 3.200MHz to 90.000 MHz, the HC49S can serve as a low cost solution in virtually any application or market.

Quartz is used in the making of sandpaper, optics, glass, liquid filters, circuit boards, computer components, cement, mortar, and jewelry. Quartz crystals are also piezoelectric meaning when an electrical current passes through them they vibrate a small amount. Time can be measured from the vibrations of the quartz crystals so quartz crystals are often used in clocks.

Quartz crystals may either operate in a fundamental mode or in an overtone mode. Below frequencies of around 25 MHz crystals are normally designed to operate in their fundamental mode, whereas above this they will normally be designed for overtone operation, although with manufacturing techniques improving higher frequency crystals are becoming available. The mode is therefore an important element of the crystal specification.

Crystal oscillators are used in a variety of applications. In some instances crystal oscillators may be used to provide a cheap clock signal for use in a digital or logic circuit. In other instances they may used to provide an RF signal source. In view of the fact that quartz crystals offer a very high level of Q and they are stable, crystal oscillators are often used in oscillator circuits to provide stable, accurate radio frequency signals.

There is a great number of different types of circuit that can be used for crystal oscillators, each one having its own advantages and disadvantages. One of the most common circuits used for crystal oscillators is the Colpitts configuration as shown below.

In this configuration, the crystal operates in a parallel mode. When running in this mode, the crystal should be presented with a load capacitance to operate on its correct frequency. This load capacitance is specified with the crystal and is typically 20 or 30 pF. The crystal oscillator circuit will be designed to present this capacitance to the crystal. Most of this will be made up by the two capacitors C1 and C2, although the remaining elements of the circuit will provide some capacitance.

Quartz crystals use the piezoelectric effect to convert the incoming electrical impulses into mechanical vibrations. These vibrations are affected by the mechanical resonances of the crystal, and as the piezoelectric effect operates in both directions, the mechanical resonances affect the electrical stimuli, being reflected back into the electrical circuit.

Today, quartz crystal filters can be designed with pass bands ranging from frequencies in the kilohertz region up to many Megahertz - with the latest technology this can rise to 100 MHz and more. However for the best performance and lowest costs the passband of the filter is generally kept to below about 30 MHz or so.

Quartz crystals have piezoelectric properties; they develop an electric potential upon the application of mechanical stress. An early use of this property of quartz crystals was in phonograph pickups. One of the most common piezoelectric uses of quartz today is as a crystal oscillator. The quartz clock is a familiar device using the mineral. The resonant frequency of a quartz crystal oscillator is changed by mechanically loading it, and this principle is used for very accurate measurements of very small mass changes in the quartz crystal microbalance and in thin-film thickness monitors.Our Kingtronics short for Kt (logo) crystals are widely used in the oversea market.

Kingtronics offers leaded quartz crystal HC49U, HC49S and SMD quartz crystal HC49SMD.

Quartz Crystals General Information

A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography. The process of crystal formation via mechanisms of crystal growth is called crystallization or solidification. The word crystal is derived from the Ancient Greek word κρύσταλλος (krustallos), meaning "rock-crystal" but also "ice", from κρύος (kruos), "icy cold, frost". The word once referred particularly to quartz, or "rock crystal".

Electronic-grade quartz crystal is single-crystal silica which has properties that make it uniquely useful for accurate frequency controls, timers, and filters in electronic circuits. These devices are utilized for a wide variety of electronic applications in communications equipment, computers, aerospace hardware, instruments for commercial use.