What Is A Crystal Oscillator? Selection Guidance
Crystal Oscillator Parameters
Crystal Oscillator Function
Crystal Oscillator Types
Crystal Oscillator Selection Guidance
Crystal Oscillator Package
Detection of Crystal Oscillator
A crystal oscillator is a kind of electronic oscillators that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a precise frequency. Generally speaking, a wafer is cut off from a quartz crystal at a certain azimuth angle, and then added IC to form an oscillating circuit inside the package is called a crystal oscillator.
As above mentioned, the resonator plate can be cut from the source crystal at different angles, so the way of the cut will influence the crystal's aging characteristics, frequency stability, thermal characteristics, and other parameters. Almost cuts are made at bulk acoustic wave (BAW); as for higher frequencies, surface acoustic wave (SAW) devices are employed.
thickness shear (c-mode, slow quasi-shear)
35°15', 0° (<25 MHz)
35°18', 0°(>10 MHz)
the most common cut, and he plate contains the crystal's x axis and is inclined by 35°15' from the z (optic) axis. The frequency-temperature curve is a sine-shaped curve with inflection point at around 25–35 °C. Has frequency constant 1.661MHzmm.
a double-rotated cut (35°15' and 21°54') for oven-stabilized oscillators.
thickness shear (b-mode, fast quasi-shear)
a special cut, which is similar to AT cut.
a double-rotated cut with improved characteristics for oven-stabilized oscillators.
a double-rotated cut with improved characteristics for oven-stabilized oscillators.
a double rotated cut with better temperature-frequency characteristics than AT and BT cuts
the frequency-temperature curve is a downward parabola.
The frequency-temperature curve is a downward parabola.
low temperature coefficient, widely used for low-frequency crystal filters.
length-width flexure (bending)
XY, tuning fork
it is smaller than other low-frequency cuts, less expensive, has low impedance and low Co/C1 ratio, and the chief application is the 32.768 kHz RTC crystal.
the temperature coefficient is linear.
cut is made of two quartz plates bonded together.
a double rotated cut.
a double rotated cut.
a double rotated cut.
a double rotated cut.
a double rotated cut (Linear Coefficient) with a linear temperature-frequency response.
temperature-sensitive, single mode with steep frequency-temperature characteristics.
the plane of the plate is perpendicular to the X axis of the crystal, it is also called perpendicular, normal, Curie, zero-angle, or ultrasonic.
The crystal oscillators are used in applications where a very stable frequency is required.
In LC and RC oscillators, the oscillator frequency changes due to change in temperature, power supply voltage or even slight change in the component values.
In the well-designed crystal oscillator, the change in the frequency is minimum with the change in different parameters.
The crystal oscillator provides very good selectivity (due to very high Q- Quality Factor)
Working of crystal oscillator:
The crystal oscillator works on the principle of inverse piezo-electric effect.
In the video, the principle has been explained and the different materials which are often used as crystal have been discussed briefly.
The quartz is most commonly used material for the crystal design.
The equivalent circuit of the crystal:
The crystal can be represented as the RLC circuit in the electrical equivalent circuit. And it has two resonant frequencies
1) The Series Resonant Frequency (fs)
2) The Parallel Resonant Frequency (fp)
The RLC circuit provides the frequent selectivity for the oscillation and when this crystal is used with the amplifier, it can be used as an oscillator.
Crystal is a solid in which consists of atoms, molecules, or ions packed in a regularly ordered, in addition, its repeating pattern extends in all three spatial dimensions.
The object made of an elastic material could be used like a crystal nearly, with an appropriate transducer, because all objects have natural resonant frequencies of vibration. For example, steel is very elastic and has a high speed of sound. It was often used in mechanical filters before quartz. The resonant frequency depends on size, shape, elasticity, and the speed of sound in the material. Generally, high-frequency crystals are cut in the shape of a simple rectangle or circular disk. Low-frequency crystals, such as those used in digital watches, are usually cut in the shape of a tuning fork.
When a crystal of quartz is properly cut and mounted, it can be made to distort in an electric field by applying voltage electrodes near or on the crystal. This property is known as piezoelectric effect. If an alternating voltage is applied to the two electrodes, the wafer will produce mechanical vibration, and then it will produce an alternating electric field. When the field is removed, the quartz generates an electric field as it returns to its previous shape, and this can generate a voltage. The process of a quartz crystal is like an RLC circuit, composed of an inductor, capacitor and resistor, with a precise resonant frequency.
Quartz has an advantage that the frequency dependence on temperature can be very low because of its elastic constants and its size change. But the specific characteristics depend on the mode of vibration and the angle at which the quartz is cut (which is related to the crystallographic axes). Thus, the resonant frequency of the plate, which depends on its size, does not change much. This means that a quartz clock, filter or oscillator can remain accurate. For critical applications the quartz oscillator is mounted in a temperature-controlled container, called a crystal oven con concretely, and can also be mounted on shock absorbers to prevent perturbation from external mechanical vibrations.
The quartz crystal oscillator is an oscillator with high precision and high stability, and the quartz crystal oscillator has sound frequency stability and anti-external interference, so it is used for generating a reference frequency. What’s more, the accuracy of the frequency in the control circuit is controlled by the reference frequency, and is widely applied to various oscillating circuits such as a color television, a computer, a remote controller and so on, and it also used in a communication system for a frequency generator and in the data processing device for generates a clock signal, or provided a reference signal for a specific system.
The crystal oscillator can be electrically equivalent to a two-terminal network with a capacitor and a resistor in parallel and a capacitor in series. In electrotechnics, this network has two resonance points: the lower frequency is the series resonance, and the higher frequency is parallel resonance. Due to the characteristics of the crystal itself, the two frequencies is quite close. In this very narrow frequency range, the crystal oscillator is equivalent to an inductor, and it will form a parallel resonant circuit as long as the appropriate capacitor at the two ends of the crystal oscillator is connected in parallel. And this parallel resonant circuit can be added to a negative feedback circuit to form a sinusoidal oscillation. Because the crystal oscillator is equivalent to the frequency of inductor and the frequency range is very narrow, even if the parameters of the other elements vary widely in the circuit, the frequency of the oscillator will not vary greatly. In addition, the crystal vibration has an important parameter, that is, the load capacitance. If a parallel capacitor with a same load capacitance of crystal oscillator is selected, the nominal resonant frequency of the crystal vibration can be obtained. Generally, the general crystal oscillator circuit is connected the crystal oscillator at both ends of a reverse amplifier, and a capacitor is connected at each end of crystal oscillator respectively(the other end of each capacitor is connected to the ground). The capacity of the two capacitors in series should be equal to the load capacitance of crystal oscillator. Note that the pins of the general IC have the equivalent input capacitance.
(1) Total frequency difference: the maximum frequency difference between the frequency of the crystal oscillator and the given nominal frequency caused by the combination of all the specified working and non-working parameters within a specified time.
Note: The total frequency difference includes the maximum frequency differences caused by frequency temperature stability, frequency temperature accuracy, frequency aging rate, frequency power-supply voltage stability and frequency load stability. Generally, it is only concerned about the short-term frequency stability, but not strictly required for other frequency stability indexes, such as precision guidance radar.
(2) Frequency temperature stability: under nominal power supply and load, the maximum allowable frequency difference without implied reference temperature or with implied reference temperature works at a specified temperature range.
FT: frequency-temperature stability (without implied reference temperature)
FTref: frequency-temperature stability (with implied reference temperature)
fmax: the highest frequency measured in the specified temperature range
Fmin: the minimum frequency measured in the specified temperature range
fref: frequency measured by specified reference temperature
Note: The results show that the production difficulty of crystal oscillator with fTref index is higher than that of crystal oscillator with fT index, so the price of crystal oscillator with fTref index is higher.
(3) Frequency stable preheating time: based on the stable output frequency of the crystal oscillator, the time required from charging to the output frequency is less than the tolerance of the specified frequency.
Note: In most applications, a crystal oscillator is operating all the time, however, in some applications, crystal oscillators frequently power-on and off. At this time, the frequency-stable preheating time should be taken into account (especially when the frequency temperature stability is required to be in the range of ≤±0.3ppm(-45℃～85℃), using OCXO as the present vibration, and the frequency stability preheating time will not be less than 5 minutes, but the DCXO will take only a few seconds.
(4) Frequency aging rate: the relationship between oscillator frequency and time when measuring oscillator frequency under constant ambient conditions. This long-term frequency shift is caused by slow changes in crystal components and oscillator circuit elements, and the maximum change at a specified time limit (e.g. ±10ppb/day, after 72 hours of power-up), Or the maximum total frequency variation (e.g. ±1ppm/(first year) and ±5ppm/(tenth year) within a specified time limit.
Note: The frequency aging rate of the TCXO is: ±0.2ppm~±2ppm(first year) and in the range of ±1ppm~±5ppm(tenth year). The frequency-aging rate of the OCXO is: ±0.5ppb~±10ppb/ day (after power on for 72 hours), and the frequency of the OCXO is ±30ppb~±2ppb (first year), and the rate of the OCXO is ±0.3ppm~±3ppm (tenth year).
(5) Frequency voltage controlled range: the minimum peak value of the crystal oscillator frequency when adjusting the frequency control voltage from the reference voltage to the prescribed terminal voltage.
Note: The results show that the reference voltage is 2.5V, the specified terminal voltage is 0.5V and 4.5V, the frequency change of the VCO is -110ppm at the +0.5V frequency controlled voltage, and the frequency change is +130ppm at the 4.5V control voltage. The voltage controlled range of VCXO is ≥±100ppm (2.5V±2V).
(6) The response range of voltage-controlled frequency: the relationship between peak frequency difference and modulation frequency when modulating frequency changes. It is usually expressed in dB with a specified modulation frequency lower than the modulation reference frequency.
Note: the response frequency voltage controlled range of VCXO is 0~10kHz.
(7) Frequency-controlled linearity: a measure between the output frequency and input controlled voltage transmission characteristic as compared to an ideal (linear) function, which is expressed as a percentage of the allowable non-linearity of the entire range frequency difference.
Note: the typical linearity of VCXO frequency voltage control is: ≤ ±10%, ≤ ±20%. The simple linear calculation method of VCXO frequency voltage control is as follows: (when the frequency voltage control polarity is positive):
Frequency-controlled linearity=±[(fmax-fmin)/ f0]×100%
fmax: output frequency of VCXO at maximum voltage-controlled voltage
fmin: output frequency of VCXO at minimum voltage-controlled voltage
F0: voltage frequency of voltage controlled center
(8) SSB phase noise ￡(f): the ratio of the power density of a phase-modulated side band to the carrier power at a deviation from the carrier f.
Frequency accuracy: at nominal power supply voltage, nominal load impedance, reference temperature (25℃) and other conditions, the maximum allowable deviation between the frequency of crystal oscillator and its nominal value, that is (fmax-fmin) /f0.
Temperature stability: with other conditions unchanged, the allowable frequency difference of the maximum variation of the output frequency of the crystal oscillator relative to the sum of the extreme values of the output frequency within the temperature range, i.e. (fmax-fmin) /(fmax fmin).
Range of frequency regulation: the range of output frequencies is changed by adjusting a variable element of the crystal oscillator.
Frequency modulation(FM) | voltage controlled characteristics: including FM deviation, FM sensitivity, FM linearity.
a. FM deviation: it refers to the output frequency difference when the control voltage of the VCO changes from the nominal maximum to the minimum.
b. FM sensitivity: the output frequency change caused by the unit of voltage controlled crystal oscillator and the control voltage.
c. FM linearity: a measure of the transmission characteristics of a modulation system compared with an ideal straight line (least square method).
Load characteristics: other conditions remain unchanged, the maximum allowable frequency deviation of the output frequency of the crystal oscillator relative to the output frequency of the nominal load within a specified range of variations.
Voltage characteristics: other conditions remain unchanged, the maximum allowable frequency deviation of the output frequency of the crystal oscillator relative to the output frequency of the nominal supply voltage within the specified range of variation of the supply voltage.
Clutter: the power ratio of the discrete spectrum component to the main frequency in the output signal which is related to the main frequency without harmonics (except sub-harmonics), expressed in dBc.
Harmonics: the ratio of harmonic component power Pi to carrier power P0, expressed in dBc.
Frequency aging: the systematic drift of the output frequency with time due to the aging of components (mainly quartz resonators) under specified environmental conditions. It is usually measured by the frequency difference within a certain interval. For highly stable crystal oscillator, because the output frequency is approximately linear in a long working time, the ageing rate (relative frequency variation per unit time) is often used to measure.
Daily fluctuation: the oscillator is measured once every hour after the specified warm-up time, and the test data is continuously measured for 24 hours, and the test data is calculated according to S = (fmax-fmin)/ f0, finally, the daily fluctuation is obtained.
Startup: the maximum change in the frequency of the oscillator within a given preheating time, expressed as V= (fmax-fmin) /f0.
Phase noise: it is the frequency domain representation of rapid, short-term, random fluctuations in the phase of a waveform, caused by time domain instabilities.
One of the main characteristics of crystal oscillator is the stability within operating temperature, which is an important factor to determine the price of oscillator. The higher the stability or the wider the temperature range, the higher the price of the device.
Crystal aging is an important factor of frequency change. Depending on the life expectancy of the target product, there are several ways to reduce the influence. Crystal aging causes the output frequency to change which reflected a logarithmic curve, and it is the most significant phenomenon in the first year of using. For example, when crystals are used for more than 10 years, the aging rate is about three times that of the first year. Fortunately, adopt special crystal can improve this situation, or it can be solved by adjusting some parameters, for example, the voltage can be applied on the control pin so on.
Other factors related to frequency stability include supply voltage, load, phase noise, jitter, electromagnetic interference (EMI), which should be indicated clearly. For industrial products, it is necessary to put forward the indexes of vibration and shock, such as aerospace equipment, tolerance needed to be marked when pressure changes or exposed to radiation, and so on.
Crystal oscillator has the output of compatible HCMOS/TTL, ACMOS, ECL and sine-wave type. Each of them has its unique waveform characteristics and uses. What’s more, attention should be paid to the requirements of three-state or complementary outputs, in addition, symmetry, rising time and falling time, and logic levels are also required for certain ranges. For example, many DSP and communication chip set often require strict symmetry (45%~55%) and rapid rising and falling time (less than 5ns).
Phase noise and jitter: phase noise measured in frequency domain is a true measure of short-term stability. It can be measured within the center frequency of the 1Hz, and usually to 1MHz. The phase noise of the crystal oscillator is improved at the frequency away from the center frequency. The TCXO and OCXO oscillators and other crystal oscillators using fundamental or harmonic modes have the best phase noise performance. The phase noise performance of the oscillator using PLL synthesizer is worse than that of oscillator without using it.
Jitter is related to phase noise, but it is measured in time domain. Jitter in picoseconds can be measured by RMS or peak-peak values. Many applications, such as communication networks, wireless data transmission, ATM and SONET, must keep an eye on both two characteristics.
The influence of power supply and load: the frequency stability of the oscillator is also affected by the voltage change and the load change of the oscillator. These effects can be minimized by properly selecting the oscillators. The designer should test the oscillator's performance against the recommended supply voltage tolerance and load. Oscillators operation at the excessive recommended supply voltage will reflect poor waveform and stability.
Specific application: the clock source of microcontroller can be divided into two categories: one is based on mechanical resonance device, such as crystal oscillator, ceramic resonance channel (Pierce oscillator configuration is suitable for them); another is RC oscillators. The crystal oscillator and ceramic resonator can usually provide very high initial precision and low temperature coefficient. The RC oscillator can start quickly and the cost is relatively low. However, its accuracy is usually low in the whole temperature and working power supply voltage range, which will change at 5% ~50% of the nominal output frequency. However, its performance is affected greatly by the environmental conditions and the selection of circuit components. It is must take serious consideration of the oscillator circuit elements selection and the circuit board layout. When using, the ceramic resonance channel and the corresponding load must be optimized according to specific logic series.
The environmental factors affecting oscillator operation include electromagnetic interference (EMI), mechanical vibration and shock, humidity and temperature. These factors increase the increase instability, and in some cases, cause oscillator damage. Most of the above problems can be avoided by using oscillator modules. These modules provide low-resistance square wave output with their own oscillators and can operate under certain conditions. The crystal oscillator module provides the same accuracy as the discrete crystal oscillator. For example, the accuracy of silicon oscillator is higher than that of discrete RC oscillator.
The following factors need to be considered in order to optimize the clock source in specific applications: precision, cost, power consumption, and environmental requirements.
Power consumption should also be considered when selecting oscillators. The power consumption of the discrete oscillator is mainly determined by the power supply current of the feedback amplifier and the capacitance value inside the circuit. The power consumption of the CMOS amplifier is proportional to the operating frequency and can be expressed as the power dissipation capacitance. For example, the power dissipation capacitance of the HC04 inverter gate circuit is 90 PF, when working under a 5V power supply of 4MHz, it is equivalent to the power current of 1.8mA, with the 20pF crystal load capacitance, the whole power supply current is 2.2mA. Ceramic resonance channels usually have larger load capacitors, so more current is needed accordingly. In contrast, the crystal oscillator module usually needs the power current of 10mA~ 60mA. The power current of the silicon oscillator depends on its type and function, ranging from microamps of low-frequency (fixed) devices to milliamps of programmable devices.
1. A general crystal oscillator is used in a variety of circuits to produce an oscillating frequency.
2. A quartz crystal resonator is used for clock pulses, which is matched with other elements to generate a standard pulse signal, and is widely used in the digital circuit.
3. Quartz crystal resonator for microprocessor.
4. CTVVTR uses a quartz crystal resonator.
5. Quartz crystal oscillator for watches and clocks.
Temperature-compensated crystal oscillator(TCXO), voltage-controlled crystal oscillator(VCXO), oven-controlled crystal oscillator(OCXO), digitally compensated crystal oscillators(DCXO), and microcomputer-compensated crystal oscillator(MCXO).
The crystal oscillator in the electronic circuit is also divided into two types: passive crystal oscillators and active crystal oscillators.
The quartz crystal oscillator can be divided into common quartz crystal oscillator, precision quartz crystal oscillator, medium-precision quartz crystal oscillator and high-precision quartz crystal oscillator according to the precision (or frequency stability). It can be divided into metal shell crystal oscillator, glass shell crystal oscillator, bakelite shell crystal oscillator and plastic shell crystal oscillator according to the package structure and shape. In addition, metal shell crystal oscillator can be divided into tin soldering, cold-pressure welding and (electric) resistance welding type. It can be divided into dual electrode crystal oscillator, three-electrode crystal oscillator and four-electrode crystal oscillator according to the number of the extraction electrode. According to the specific apllications: crystal oscillator for color TV, crystal oscillator for DVD player, crystal oscillator for wireless communication, crystal oscillator for electronic clock, etc. According to the basic resonance circuit, it can be divided into two types: parallel crystal oscillator and series crystal oscillator.
Common Types and Its Abbreviations
analog temperature controlled crystal oscillator
calibrated dual crystal oscillator
digital temperature compensated crystal oscillator
digitally compensated crystal oscillator
evacuated miniature crystal oscillator
global positioning system disciplined oscillator
microcomputer-compensated crystal oscillator
oven-controlled voltage-controlled crystal oscillator
oven-controlled crystal oscillator
rubidium crystal oscillators (RbXO)
temperature-compensated voltage-controlled crystal oscillator
temperature-compensated crystal oscillator
tactical miniature crystal oscillator
temperature-sensing crystal oscillator
voltage-controlled temperature-compensated crystal oscillator
voltage-controlled crystal oscillator
The difference between active crystal oscillator and passive crystal oscillator
Passive crystal oscillator requires an oscillator in the CPU. There are only two pins without power-supply voltage, therefore, its signal level is determined according to the starting vibration circuit, and the same crystal vibration can be applied to various voltages and can be used for the CPU with different voltage requirements. In general, the price of passive crystal oscillators is relatively low, and in the civil products, it is applied to reduce the cost.
An active crystal oscillator is a complete oscillator with quartz crystals, transistors, and resistive and capacitive elements.
1. Passive crystal oscillator is a non-polar element with two pins. It can produce oscillation signal only by means of clock circuit, because it can't oscillate itself.
2. The active crystal oscillator has four pins and is a complete oscillator. It has the quartz crystal, transistors and resistive elements which mainly look at the circuits you apply. If there is a clock circuit, it is suitable to use passive crystal oscillator in the circuit design.
1. The passive crystal needs the oscillator in the DSP chip, but it has no voltage problem, the signal level is variable, that is to say, it is determined by the starting circuit, and the same crystal can be applied to a variety of voltages, also can be used for many different clock signal voltage requirements of DSP and the price is usually lower.
2. The active crystal oscillator does not need the internal oscillator of DSP, because its signal quality is good and stable, moreover its connection way is relatively simple (usually uses a capacitor and the inductor to form PI type filter network, and the output end with a small resistor to filter the signal), do not require complex configuration.
Conclusion: the defect of passive crystal relative to crystal oscillator is that the signal quality is poor and the peripheral circuits (capacitors, inductors, resistors, etc.) usually need to be accurately matched. The peripheral configuration circuit needs to be adjusted when changing different frequency crystals. It is suggested that quartz crystal with high precision should be used, and ceramic crystal with low precision should not be used as far as possible.
The active crystal oscillator does not need the internal oscillator of CPU, the signal is stable, the quality is good, and the connection mode is relatively simple (mainly to do the power source filter well, usually using a PI filter network composed of capacitance and inductance. Output with a small resistance to filter the signal), do not need a complex configuration circuit.
Compared with the passive crystal, the shortcoming of the active crystal oscillator is that the signal level is fixed, so its flexibility is poor, and the price is relatively high. For the application of sensitive timing requirements, it is better to use active crystal oscillator, so we can choose more precise crystal oscillator, or even high-grade TCXO. Some CPU have no starting circuit and can only use active crystal oscillators. Compared with the passive crystal, the active crystal oscillator is usually larger in volume. Many active crystal oscillations are surface-mount and have the same volume as the crystals, but some are smaller than many crystals.
The crystal oscillator is widely used in communication equipment, microwave communication equipment, SPC telephone exchange, GSM MS service test set, BP machine, mobile telephone launching pad, high-grade frequency counter, GPS, satellite communication, remote control mobile equipment and so on. If the device needs to be out-of-the-box, you must select a VCXO or a TCXO, and if the requiring stability is above 0.5ppm, a MCXO needs to be selected. analog temperature controlled crystal oscillator(ATCXO) is suitable for the requirement of the stability between 5ppm and 0.5ppm. The VCXO is only suitable for products with stability requirements below 5ppm. OCXO may be used if signal stability is required to exceed 0.1ppm in an out-of-the-box environment.
When the device is selected, it is necessary to ensure the reliability of the product. The selection of higher-grade devices can further reduce the failure and lead to potential benefits, which is also taken into account when comparing the prices of the products. To pursuit a balanced and reasonable performance of oscillators, this requires a trade-off of factors such as stability, operating temperature, crystal aging effect, phase noise, cost, and so forth, where the cost is not only the price of the device, but also the use cost of the product's full service life.
Crystal oscillators are typically encapsulated in metal cases, also in glass, ceramic, or plastic packages.
The practical environment of the crystal oscillator's application needs to be carefully considered. For example, high-strength vibration or shock can cause problems with the oscillator, except that the possibility of physical damage, it may cause an erroneous action at some frequency. These external induced disturbances will result in frequency hopping, increasing noise, and intermittent oscillator failure. EMI is another priority to be considered for applications that require special EMI compatibility. It is necessary to use a suitable pc motherboard layout technique, and select a clock oscillator that provides a minimum amount of radiation. Generally, an oscillator with a slower rising/ falling time has a better EMI feature.
1. miniaturization, thinning, and lamination (the packaging of quartz crystal oscillators has changed from traditional bare metal case to plastic and ceramic packaging).
2. high precision and high stability.
3. low noise, high frequency.
4. low power consumption, fast start-up (low voltage operation, low level drive and low current consumption).
Common faults in the crystal oscillator include:
(a) Internal leakage
(b) Internal open-circuit
(c) Metamorphic frequency deviation
(d) Leakage of external capacitor connected to it
Testing the quartz crystal oscillators, first is check the appearance, the surface of it is clean, no crack, its pin is firm and reliable, and the resistance value is infinite. If the resistance measured with a multimeter is small or even close to zero, it is indicated that the leakage or breakdown of the measured crystal, or the crystal oscillator has been damaged. If the measured resistance is infinite, it is indicated that the quartz crystal has no breakdown and leakage, but it is not possible to conclude whether the crystal is damaged. At this time, the capacitance value of the quartz crystal can be further detected according to different frequencies by the digital multimeter, and the data can be used to determine whether the quartz crystal is damaged or not compared with the normal values on the instruction. Several common methods for detecting crystal vibration are as follows.
1) Resistance measurement
The positive and reverse resistance values of quartz crystal oscillator measured by multimeter R × 10k level should be infinite under normal condition. If the quartz crystal oscillator has a certain resistance value or zero, it indicates that the quartz crystal oscillator has leakage or breakdown damage. On the contrary, if the resistance value measured by multimeter is infinite, the quartz crystal may not be sound as judgement. At this time, another method can be used to further judge the quartz crystal.
2) Capacitance measurement
Measure the capacitance of the quartz crystal oscillator by using the capacitance meter or the digital multimeter, it can roughly judge whether the quartz crystal oscillator is good or not. For example, the capacitance approximations of 45kHz, 480kHz, 500kHz and 560kHz quartz crystal oscillators commonly used in remote control transmitters are 296~310pF, 350~360pF, 405~430pF, 170-196pF, respectively. If the measured capacitance of the quartz crystal oscillator is larger than approximate value or no zero, it can be determined that the quartz crystal oscillator is damaged.
3) Test circuit detection
A common method for quartz crystal detection is to make a simple oscillating circuit(the two leads of the quartz crystal oscillator cannot be too close to each other) to see whether exist oscillation. If they start to vibrate, showing that the crystal is good, otherwise it is bad.
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