somewhatElectronic equipmentNeed highly stable frequencyAC signal, and LCoscillatorThe stability is poor, and the frequency is easy to drift (i.e. the generated ACsignal frequency Easy to change).Use a special element in the oscillator——quartz crystal, which can produce highly stable signals. This oscillator using quartz crystal is called crystal oscillator.[1]
Chinese name
crystal oscillator
Foreign name
crystal oscillator[1]
Abbreviation
Crystal oscillator[1]
Composition
quartz[1]
Purpose
Electrical appliances, communication equipment, etc
stayquartz crystalCut off the sheet in a certain direction, polish both ends of the sheet and coat them with conductive silver layer, then connect two electrodes from the silver layer and seal them. This component is calledQuartz crystal resonator, quartz crystal for short.The shape, structure and graphic symbols of quartz crystal are shown in Figure 1.[1]
Figure 1[1]

Fig. 1 Quartz crystal[1]
2. Characteristics[1]
There are two quartz crystalsresonant frequency , i.e. fs and fp, fp is slightly larger than fs.When the frequency of signals added to both ends of quartz crystal is different, it will show different characteristics, as shown in Figure 2, and the details are as follows.[1]
Figure 2[1]

Fig. 2 Characteristics of quartz crystal[1]
① When f=fs, the quartz crystal is resistive, which is equivalent to a small resistance.[1]
② When f ≥ fp, quartz crystal is capacitive, equivalent to capacitance.[1]
Circuit symbol
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Crystal oscillator iselectronic circuit It is one of the most commonly used electronic components in. It is generally represented by the letters "X", "G" or "Z", and the unit is Hz.Crystal oscillatoryGraphical symbolsAs shown in Figure 3.[2]
Figure 3[2]
Figure 3 Graphic Symbols of Crystal Oscillator[2]
form
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Crystal oscillator is mainly composed ofcrystalAnd peripheral components.Figure 4 shows the physical shape, internal structure and circuit of the crystal oscillatorGraphical symbolsandequivalent circuit 。[3]
Figure 4[3]

Figure 4 Physical shape and internal structure of crystal oscillator, circuit graphic symbols and equivalent circuit[3]
working principle
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Crystal oscillator hasPiezoelectric effectThat is, the crystal will deform after the applied voltage at the two poles of the chip. Conversely, if the external force deforms the chip, the metal chip at the two poles will generate voltage.If appropriateAlternating voltage, the chip will produceresonance(resonant frequency vs. quartzInclined planeInclination is related, and the frequency is certain).Crystal oscillator uses a kind of energy tomechanical energyThe mutually transformed crystals can work in resonance state to provide stable and accurateSingle frequency oscillation。In generalWorking conditionsThe absolute precision of ordinary crystal frequency can reach 50 parts per million.With this feature, crystal oscillator can provide more stable pulse, which is widely used inMicrochipOfClock circuitLi.Most wafers are quartzsemiconductor material , for housingMetal packaging。[2]
The crystal oscillator is usually connected with the main boardSouth Bridge, sound card, etc.Crystal oscillator can be compared to the "heartbeat" of each boardGeneratorIf there is a problem with the "heartbeat" of the main card, other circuits will fail.[2]
classification
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1. Parallel crystal oscillator[1]
The parallel crystal oscillator is shown in Figure 5.triodeVT is composed of R1, R2, R3 and R4Amplification circuit；C3 is ACBypass capacitance, YesAC signalEquivalent to short circuit;X1 is quartz crystal, which is equivalent to inductance in the circuit.It can be seen from the AC equivalent diagram that the circuit is aCapacitance three-point oscillatorC1, C2 and X1 form a frequency selection circuit, whose frequency selection is mainly determined by X1, and the frequency is close to fp.[1]
Figure 5[1]

Fig. 5 Parallel crystal oscillator[1]
Circuit oscillation process: after the power supply is turned on, the triode VT is turned on, and the varying Ic current flows through VT, which contains weak signals of 0~∞ various frequencies.These signals are added to the frequency selection circuit composed of C1, C2 and X1, from which f0 signals are selected. There is f0 signal voltage at both ends of X1, C1 and C2, and f0 signals at both ends of C2 are takenVoltage feedbackTo the base emitter of VT for amplificationoutput signalWhen it is added to the frequency selection circuit, the signal voltage at both ends of C1 and C2 increases, and the voltage at both ends of C2 is sent to the VT base emitter. Repeat this process, the VT output signal becomes larger and largerMagnificationGradually decrease when the magnification of the amplification circuit is equal toFeedback circuitOfAttenuation coefficientWhen equal, the output signal amplitude remains stable and will not increase again, and the signal will be sent to other circuits.[1]
2. Series crystal oscillator[1]
Series crystaloscillatorAs shown in Figure 6.The oscillator uses a two-stage amplification circuit. In addition to forming a feedback circuit, the quartz crystal X1 also has the function of frequency selection. Its frequency selection f0=fs,potentiometerRP1 is used to adjust the amplitude of the feedback signal.[1]
Figure 6[1]

Fig. 6 Series crystal oscillator[1]
(1) Judge the type of feedback circuit[1]
Because the signal is fed back to VT1EmitterNow it is assumed that the instantaneous polarity of VT1 emitter voltage is "+",collectorVoltage polarity is "+" (emitter and collector arein-phaseWhen the emitter voltage rises, the collector voltage also rises)BaseThe voltage polarity is "+", and the emitter voltage polarity is also "+". The voltage of this polarity is fed back to the emitter of VT1 through X1. The feedback voltage polarity is the same as the assumed voltage polarity, so the feedback ispositive feedback。[1]
(2) Oscillation process of circuit[1]
After the power supply is turned on, the triode VT1 and VT2 are turned on, and the changing Ie current output by the VT2 emitter contains signals of various frequencies. The quartz crystal X1 has a very small impedance to the f0 signal, and the f0 signal is fed back to the emitter of VT1 through X1 and RP1. The signal is amplified by VT1 and output from the collector, then added to VT2 and output from the emitter, and then fed back to VT1 for amplification through X1,Repeat this process, the amplitude of f0 signal output by VT2 becomes larger and larger, and the magnification of the amplification circuit composed of VT1 and VT2 becomes smaller and smaller. When the magnification is equal to the feedback attenuation coefficient, the amplitude of the output f0 signal will not change, and the circuit will output a stable f0 signal.[1]
threeQuartz crystal oscillatorIt is divided into non temperature compensated crystal oscillator and temperature compensated crystal oscillator（TCXO）、voltage control Crystal oscillator（VCXO）Constant temperature controlled crystal oscillator（OCXO）And digitization/μP Compensated crystal oscillator (DCXO/MCXO).Among them, the non temperature compensated crystal oscillator is the simplest oneJapanese Industrial Standard（JIS）It is called standard packaged crystal oscillator (SPXO) in.[2]
① Thermostatically controlledcrystalOscillator.The thermostatically controlled crystal oscillator (OCXO) usesIncubation bathTo make a crystal oscillator or quartz crystalVibratorThe temperature of is kept constant, and the oscillator caused by the surrounding temperature changeoutput frequency The crystal oscillator whose variation is reduced to the minimum is shown in Figure 15-3.In OCXO, some only place the quartz crystal oscillator in the constant temperature bath, some place the quartz crystal oscillator and related important components in the constant temperature bath, and some place the quartz crystal oscillator in the internal constant temperature bathOscillating circuitIt is carried out in the external constant temperature bathtemperature compensationDouble thermostatic bath control method is adopted.utilizeProportional controlThe constant temperature bath ofStabilityIncrease to more than 5000 times, so that the oscillatorFrequency stabilityKeep at least 1 × 10-9.OCXO is mainly used for mobile communicationBase station, national defense, navigationFrequency meterCounter, spectrum andnetwork analyzer And other equipment and instruments.OCXO is composed of thermostatic bath control circuit and oscillator circuit.Usually people useThermistor“bridge”ConstitutivedifferentialSeries amplifiertemperature controlOf.haveautomatic gain controlThe (Clapp) oscillation circuit of (AGC) is ideal for obtaining high stability of oscillation frequency in recent yearsTechnical proposal。In recent years, the technical level of OCXO has been greatly improved.[2]
Figure 15-3[2]

Figure 15-3 Shape of thermostatically controlled crystal oscillator[2]
② Temperature compensated crystal oscillator.Temperature compensated crystal oscillator (TCXO)Temperature compensation circuitA quartz crystal oscillator that reduces the amount of oscillation frequency change generated by the ambient temperature change, as shown in Figure 7.In TCXO, the frequency of quartz crystal oscillatortemperature drift There are mainly two types of compensation methods: direct compensation and indirect compensation:[2]
Figure 7[2]

Fig. 7 Temperature controlled compensated crystal oscillator[2]
a. Direct compensation type.Direct compensation TCXO is composed ofThermistorA temperature compensation circuit composed of a resistance capacitance element and a quartz crystal oscillator is connected in series in an oscillator.When the temperature changes, the resistance of the thermistor and the capacitance of the equivalent series capacitance of the crystal change correspondingly, so as to offset or reduce the temperature drift of the oscillation frequency.The compensation circuit is simple, the cost is low, and printing is savedCircuit board（PCB）Size and space for small and low voltageSmall currentOccasion.But when the accuracy of crystal oscillator is required to be less than ± 1 × 10-6, the direct compensation method is not suitable.[2]
b. Indirect compensation type.The indirect compensation type is divided into analog type and digital type.Analog indirect temperature compensation uses temperature sensing elements such as thermistors to form a temperature voltage conversion circuit, and applies the voltage to a crystal oscillator connected in seriesVaractor diodeUpper, connected in series through crystal oscillatorCapacitanceThe change ofFrequency driftMake compensation.This compensation method can achieve ± 0.5 × 10-6 high precision, but it is limited under the low voltage below 3V.Digital indirect temperature compensation is to add a level of A/D after the temperature voltage conversion circuit in the analog indirect temperature compensation circuit（A/D）converter, willAnalog quantityconvert toDigital quantity。This method can realize automatic temperature compensation, which makes the frequency stability of crystal oscillator very high. However, the specific compensation circuit is complex and the cost is also high, which is only applicable to base stations and radio stations that require high-precision.[2]
③ Ordinary crystal oscillator.The ordinary crystal oscillator (SPXO) is a simple crystal oscillator, usually calledChime。It is a crystal oscillator that works completely by free oscillation of crystal.This kind of crystal oscillator is mainly used in occasions where the stability requirements are not high.Figure 8 shows an ordinary crystal oscillator.[2]
Figure 8[2]

Figure 8 Common Crystal Oscillator[2]
④ Voltage controlled crystal oscillator.The voltage controlled crystal oscillator (VCXO) is controlled by applying externalcontrol voltageA quartz crystal oscillator that makes the oscillation frequency variable or can be modulated.In a typical VCXO, the frequency of the quartz crystal oscillator is "pulled" by tuning the voltage to change the capacitance of the varactor diode.VCXO allowable frequencyControl rangeIt is relatively wide, and the actual traction range is about ± 200 × 10-6 or more.If VCXO output is requiredFrequency ratioThe frequency that quartz crystal oscillator can achieve is even higher, so frequency doubling scheme can be adopted.Another way to extend the tuning range is to mix the output signal of the crystal oscillator with the output signal of the VCXO.Compared with a single oscillator, the tuning range of the two heterodyne oscillators is significantly extended.[2]

characteristic
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Crystal oscillator has positiveInverse piezoelectric effectThis physical characteristic can produce very weak periodic oscillation signals, which can be used assignal sourceuse.[5]
Model designation and main parameters
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1. The model designation of the crystal oscillator is generally composed of three parts, namely, the shape and material of the shellQuartz flakeSlice type, main properties andOverall dimension, as shown in Figure 9.[2]
Figure 9[2]

Fig. 9 Naming of crystal oscillator[2]
The first part is the shape and material of the shell.J stands for metal shell.[2]
The second part is quartz chip type, which is represented by letters.F refers to FT cutting mode.[2]
The third part is the main functions and overall dimensions, which are represented by numbers.5.000 meansresonant frequency It is 5MHz.[2]
Therefore, JF5.000 means F cutting method, metal shellresonanceResonant crystal oscillator with frequency of 5MHz.[2]
For the convenience of the reader, Table 1 and Table 2 respectively list the comparison table of the shape and material letter meaning of the crystal oscillator shell, and the comparison table of the letter meaning of the representation method of the quartz chip model.[2]
Table 1 Comparison Table of Shape and Material Letter Meaning of Crystal Oscillator Shell[2]
Table 1 Comparison Table of Shape and Material Letter Meaning of Crystal Oscillator Shell[2]

Table 2 Comparison Table of Letter Meaning for Representation Method of Quartz Slice Type[2]
Table 2 Comparison Table of Letter Meaning for Representation Method of Quartz Slice Type[2]

2 Main parameters of crystal oscillator The main parameters of crystal oscillator are nominal frequencyLoad capacitance, frequency accuracyFrequency stabilityThese parameters determine the quality and performance of the crystal oscillator.Therefore, appropriate crystal oscillators should be selected according to specific requirements in practical applications, such asCommunication network、wireless data transmission Such systems need crystal oscillators with high accuracy.However, because the higher the performance of the crystal oscillator, the more expensive the price is, so you can choose the crystal oscillator that meets the requirements when you buy it.[2]
① Nominal frequency.Different crystal oscillators have different nominal frequencies, and the nominal frequencies are mostly marked on the crystal oscillator shell.[2]
② Load capacitance.The load capacitance refers to that the two leads of the crystal oscillator are connectedIntegrated circuit(IC) The sum of all effective internal and external capacitances can be regarded asCrystal oscillatorConnect capacitors in series in the circuit.Load capacitance is different,oscillatorOfoscillation frequency Different.However, the load capacitance of crystal oscillators with the same nominal frequency may not be the same.Generally, there is low load capacitance（Series resonanceCrystal) and high load capacitance（Parallel resonanceCrystal).Therefore, when the crystals with the same nominal frequency are exchanged, the load capacitance must be consistent, and they cannot be exchanged easily, otherwise the circuit will work abnormally.[2]
④ TemperatureStability。Temperature stability refers to the crystal oscillator within the specified temperature range when other conditions remain unchangedoutput frequency The allowable frequency offset value of the maximum change of (fmax fmin)/(fmax+fmin) relative to the sum of output frequency extremes within the temperature range.[2]
⑤ FrequencyAdjustment range。The range of output frequency can be changed by adjusting a variable element of the crystal oscillator.[2]
⑥Load characteristics。When other conditions remain unchanged, the maximum allowable output frequency of the crystal oscillator relative to the output frequency under the nominal load within the specified variation rangefrequency offset。[2]
⑦Voltage characteristics。When other conditions remain unchanged, the maximum allowable frequency deviation of the crystal oscillator output frequency from the output frequency under the nominal power supply voltage within the specified variation range.[2]
⑧ Clutter.Clutter refers tooutput signalMedium and main frequency noneharmonic(except for subharmonics)Discrete spectrumThe power ratio of the component to the dominant frequency, expressed in dBc.[2]
⑩ Daily fluctuation.It means that the oscillator has passed the specifiedWarm up timeAfter that, measure every 1h,Continuous measurement24h, settest dataCalculate by S=(fmax fmin)/f0 to get the daily fluctuation.[2]
Resistance measurement method: pointer typeA multimeterPlace it in R × 10k gear, connect the two pins of the crystal with a probe, and measure the resistance of the normal crystalInfinity；If the resistance value is too small, it indicates that the crystal has leakage or short circuit (Figure 10, Figure 11).[2]
capacitanceMeasurement method: The crystal is similar to a small capacitor in structure, so it can be usedCapacitance meterMeasure the capacity of the crystal, and judge whether it is normal by the capacity value of the measured sum (Figure 12).Table 3 shows the capacity of commonly used crystalsreference value。[2]
Figure 12[2]

Figure 12 Digital Meter Crystal Measurement[2]
Table 3 Capacity reference values of commonly used crystals[2]
Table 3 Capacity reference values of commonly used crystals[2]
application
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1. Crystal oscillator circuitcolour tv setApplication in circuit[4]
Crystal oscillator circuit in color TV is generally used forSystem controlIn the circuit and decoding circuit, Figure 13 shows the system control in a typical color TV circuitCircuit diagramAs shown in Figure 14Physical picture。In Figure 14, the crystal andmicroprocessor（CPU）To form crystalsOscillating circuitTo provide clock oscillation signal for CPU circuit.[4]
Figure 13[4]

Figure 13 System control circuit diagram in typical color TV circuit[4]
Figure 14[4]

Figure 14 Physical diagram of crystal oscillator circuit in typical color TV circuit[4]
2. Application of crystal oscillator circuit in computer motherboard[4]
Crystal oscillator circuit is also common on the computer motherboard, mainly including clock crystal oscillator circuit, real-time crystal oscillator circuit, sound card crystal and network card crystal. Figure 15 shows the circuit structure and physical diagram of the clock crystal oscillator circuit in the computer motherboard.[4]
Figure 15[4]

Figure 15 Circuit structure and physical drawing of clock crystal oscillation circuit in computer motherboard[4]
The crystal is a 14.318 MHzQuartz resonatorIt is mainly used as the resonant element of the oscillation circuit to convert the voltage into the corresponding frequency signal and transmit it to various types of signals on the main boardsignal processing Chip.As shown in Figure 7Clock chipCrystal oscillator circuitSketch MapThe oscillating circuit is inside the chip, and the resonant crystal is connected outside the chip.This circuit is called crystal oscillator, or crystal oscillator for short.[4]
Figure 16[4]

Figure 16 Schematic diagram of clock chip power crystal oscillator circuit[4]
3. Application of crystal oscillator circuit in induction cooker[4]
As shown in Figure 17Electromagnetic furnaceThe circuit diagram of crystal oscillator is commonly used in the circuit. In the circuit of induction cooker, the crystal oscillator is commonly used as a microprocessor (ormicro controller）Ofclock signalSource and clock signal are indispensable for the operation of the whole machine. If there is no clock signalmicroprocessorWill not start and work.[4]
Figure 17[4]
Figure 17 Circuit diagram of common crystal oscillator in induction cooker circuit[4]
