Basic principle and characteristics of Crystal Oscillator

Basic principle and characteristics of Crystal Oscillator Generally, the crystal oscillator uses the capacitor three-end (kobiz) AC equivalent oscillator circuit of 1A. The actual crystal oscillator exchange equivalent circuit 1B, where CV is used to adjust the oscillation frequency, generally, it is implemented by using a variable-capacity diode with different reverse voltage, which is also the mechanism of voltage control. The equivalent circuit of the crystal replaces the 1C after the crystal. Among them, CO, C1, L1 and RR are equivalent circuits of crystals. From the analysis of the entire oscillating slot path, we can see that it is limited to use CV to change the frequency: c = CBE, CCE, the CV three capacitors are connected in series and then connected in parallel with CO and C1. It can be seen that the smaller the C1, the larger the CO, and the smaller the effect of the CV change on the whole channel capacitor. Therefore, the frequency range of "voltage control" is smaller. In fact, since C1 is very small (1e-15 magnitude), Co cannot be ignored (1e-12 magnitude, several PF ). Therefore, when the CV becomes larger, the function of reducing the slot frequency becomes smaller and smaller. When the CV becomes smaller, the function of increasing the slot frequency increases. On the one hand, this produces a non-linear voltage control feature. The larger the voltage control range, the more nonlinear it is. On the other hand, the feedback voltage (the voltage on the CBE) to the oscillation is getting smaller and smaller, and finally the vibration is stopped. The larger the frequency, the smaller the equivalent capacitor C1. Therefore, the smaller the frequency range. Crystal Oscillator indicators Total frequency difference: the maximum deviation between the crystal oscillator frequency and the given nominal frequency caused by the combination of all the specified operating and non-working parameters within the specified time period. Note: The total frequency difference includes the maximum frequency difference caused by frequency temperature stability, frequency aging rate deviation, frequency and voltage characteristics, and frequency load characteristics. It is generally used only when it is concerned about the short-term frequency stability, but not strictly required for other frequency stability indicators. For example, precision guidance radar. Frequency Stability: Any crystal oscillator, the frequency instability is absolute, the degree is different. Curve 2 in which the output frequency of a crystal oscillator changes with time. The figure shows three factors with unstable frequency: aging, floating, and transient stability. Figure 2 crystal oscillator output frequency varies with time Curve 1 is measured once every 0.1 seconds, showing the short stability of the crystal oscillator; curve 3 is measured once every 100 seconds, showing the crystal oscillator drift; curve 4 It is measured once a day. Represents the aging of the crystal oscillator. Frequency and Temperature Stability: the maximum allowable frequency deviation that works within the specified temperature range without an implicit or implicit reference temperature under the nominal power supply and load. FT = ± (fmax-fmin)/(fmax + fmin) Ftref = ± MAX [| (fmax-fref)/fref |, | (Fmin-fref)/fref |] FT: frequency and Temperature Stability (without implicit reference temperature) Ftref: frequency temperature stability (with implicit reference temperature) Fmax: specifies the maximum frequency tested within the temperature range. Fmin: specifies the minimum frequency tested in the temperature range. Fref: Specifies the frequency of the benchmark Temperature Measurement English version (ftref indicator of the crystal oscillator is more difficult to produce than the FT indicator of the crystal oscillator, so ftref indicator of the crystal oscillator prices higher. Boot characteristics (frequency and stable warm-up time): refers to the change rate of the frequency from a period of time (such as 5 minutes) after the boot to another period of time (such as 1 hour) after the boot. It indicates the crystal oscillator reaches a stable speed. This indicator is useful for frequently-switched instruments such as frequency meters. Note: In most applications,Crystal OscillatorHowever, in some applications, crystal oscillator requires frequent power-on and shutdown, in this case, the frequency stability preheating time indicators need to be taken into account (especially for military communication stations used in harsh environments, when the frequency temperature stability is required ≤ + 0. 3ppm (-45 ℃ ~ 85 ℃), the use of ocxo as the local vibration, the frequency of stable preheating time will not be less than 5 minutes, and the use of mcxo only takes more than 10 seconds ). Frequency Aging Rate: the relationship between the oscillator frequency and time when the oscillator frequency is measured in a constant environment. This long-term frequency drift is caused by the slow changes of the crystal element and the oscillator circuit element. Therefore, the frequency offset rate is called aging rate, the maximum change rate after the specified time limit (for example, ± 10ppb/day, after 72 hours of power-on), or the maximum total frequency change within the specified time limit (for example, ± 1ppm/(the first year) and ± 5ppm/(10 years. The aging of crystals is caused by stress, pollutants, residual gases, and structural process defects during crystal production. Stress can be stabilized only after a period of change. A crystal cutting method called "stress compensation" (SC Cutting Method) has better characteristics of the crystal. The molecules of pollutants and residual gases will be deposited on the crystal film or oxidized by the crystal electrode. The higher the oscillation frequency, the thinner the crystal film used. The more powerful the effect is. This effect takes a long period of time before it becomes more stable, and this stability repeats with changes in temperature or working state-so that pollutants are concentrated or dispersed on the crystal surface. Therefore, a low-frequency crystal oscillator is better than a high-frequency crystal oscillator, a long-time crystal oscillator than a short-time crystal oscillator, and a continuous-working crystal oscillator than a intermittently working crystal oscillator. Note: The Frequency Aging Rate of tcxo is ± 0. 2ppm ~ ± 2ppm (first year) and ± 1ppm ~ ± 5ppm (ten years) (except in special cases, tcxo seldom uses metrics for The Daily aging rate, because even under laboratory conditions, the frequency change caused by the temperature change will also greatly exceed the temperature compensation crystal oscillator's daily frequency aging, so this indicator has lost its practical significance ). The aging rate of ocxo frequency is: ±0. 5ppb ~ ± 10ppb/day (72 hours after power-on), ± 30ppb ~ ± 2ppm (first year), ± 0. 3ppm ~ ± 3ppm (10 years ). Transient Stability: short-term stability. The observed time is 1 ms, 10 ms, 100 MS, 1 s, and 10 s. The output frequency of the crystal oscillator is affected by the internal circuit (Q value of the crystal, noise of components, stability of the circuit, and working state), resulting in wide spectrum instability. After measuring a series of frequency values, use the Allen equation for calculation. Phase Noise can also reflect Transient Stability (with special instruments ). Reproducibility: Definition: shutdown after a crystal oscillator has been operating stably for a long period of time, T1 (for example, 24 hours), T2 (for example, 4 hours), and F1, stop T1 again for the same period of time, then start T2 for the same period of time, and measure the frequency of F2. Reproducibility = (f2-f1)/F2. Frequency Voltage Control Range: Adjust the frequency control voltage from the reference voltage to the specified end voltage,Crystal OscillatorThe minimum peak value of the frequency. Note: The reference voltage is + 2.5 V, and the specified end voltage is + 4.5 V and + 2ppm v. When the Voltage Controlled Crystal Oscillator controls the voltage at + V frequency, the frequency changes, when the frequency change is + 1ppm when the voltage is controlled at a frequency of + 2ppm V, the voltage control range of vcxo voltage control frequency is ≥± (2.5v ± 2 v), and the slope is positive, linear Value: + 2.4%. Frequency Response range: the relationship between the peak frequency offset and the modulation frequency when the modulation frequency changes. It is usually expressed in a number of DB with a specified modulation frequency lower than the specified modulation benchmark frequency. Note: The frequency response of vcxo frequency voltage control ranges from 0 ~ 10 kHz. Frequency-controlled Linearity: output frequency compared to the ideal (straight line) function-a measure of the Voltage Transmission Characteristics of input control. It represents the allowable nonlinear degree of frequency offset across the entire range in percentages. Note: The typical vcxo frequency voltage-controlled linearity 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 control Fmin: the output frequency of vcxo at the minimum voltage controlled. F0: voltage frequency of the Voltage Control Center Single-Band Phase Noise Ratio (F): Ratio of the power density of a phase-modulated side to the power of the carrier when the carrier F is deviated. Output Waveform: the output waveform can be divided into two categories: Square Wave and sine wave. The square wave is mainly used for the clock of the digital communication system. It has the output level, duty cycle, rise/fall time, drive capacity and other indicators. With the rapid development of science and technology, similar systems such as communication, radar, and high-speed data transmission require high-quality signal sources as carriers of increasingly complex baseband information. Because a carrier signal with parasitic Amplitude Modulation and phase adjustment (non-clean signal) is modulated by a baseband signal containing information, under these ideal conditions, the nonexistent spectrum components (parasitic modulation in the carrier) will cause significant deterioration in the signal quality and data transmission error rate. Therefore, as the carrier of the transmitted signal, the cleanliness (spectrum purity) of the carrier signal has a direct impact on the communication quality. For sine waves, indicators such as harmonic, noise, and output power are usually required. Crystal Oscillator category The crystal oscillator can be divided into the following four categories based on different functions and implementation technologies: 1) Thermostatic crystal oscillator (ocxo) This type of crystal oscillator uses the constant temperature groove technology for the solution of temperature stability. The crystal is placed in the constant temperature slot. By setting the constant temperature work point, the tank remains in the constant temperature State and is not affected by the external temperature within a certain range, achieve stable output frequency. This typeCrystal OscillatorIt is mainly used in various types of communication equipment, including switches, SDH transmission equipment, mobile communication direct-release machine, GPS receiver, radio station, digital TV and military equipment. This type of crystal oscillator can contain Voltage Controlled pins as needed. Figure 3 shows how ocxo works: Figure 3 schematic diagram of a thermostatic Crystal Oscillator The main advantage of ocxo is that due to the adoption of the thermostat technology, the frequency and Temperature Characteristics in all typesCrystal OscillatorIs the best, because the circuit design is precise, its short stability and phase noise are good. The main disadvantage is that the power consumption is high and the volume is large. It takes about 5 minutes to heat up for normal operation. The typical indicators of the crystal oscillator produced by our company are as follows: 2) temperature compensated crystal oscillator (tcxo ). The temperature stability solution adopts some temperature compensation methods. The main principle is to control the temperature information after appropriate changes by sensing the ambient temperature.Crystal OscillatorTo achieve stable output frequency. Traditional tcxo uses simulator parts for compensation. With the development of the compensation technology, many large digital compensation tcxo began to emerge. This digital compensation tcxo is also called dtcxo, we call it mcxo when using single-chip microcomputer for compensation. Thanks to the digital technology, the re-temperature characteristics of this type of Crystal Oscillator have achieved high accuracy and can adapt to a wider operating temperature range, it is mainly used in military fields and in harsh environments. With the joint efforts of a large number of R & D personnel, our company independently developed the high-precision mcxo. Its Design Principle and world-leading, with a highly automatic production and testing system, its monthly production can reach 5000, and its design principle is 4. Figure 4 schematic diagram of the mcxo digital complementary Crystal Oscillator Typical application indicators of this type of crystal oscillator are as follows: 3) Common crystal oscillator (spxo ). This is a simpleCrystal OscillatorIt is usually called zhongzhen. The working principle is to remove the "voltage control", "Temperature Compensation", and "AGC" sections in Figure 3, which are completely completed by the Free oscillation of the crystal. This type of crystal oscillator is mainly used in scenarios with low stability requirements. 4) Voltage Controlled Crystal Oscillator (vcxo ). This is based onCrystal OscillatorWhether to use the voltage control function for classification. A type of Crystal Oscillator with voltage control input pins is vcxo. The above three types of crystal oscillator can contain pressure control ports.

Characteristics of Z Crystal Oscillator

The Z crystal oscillator is a high-precision and high-stability Oscillator. It is widely used in color TV, computer, remote control, and other oscillating circuits, it is used in communication systems for frequency generators, generates clock signals for data processing devices, and provides benchmark signals for specific systems. I. Basic principles of Z Crystal Oscillator 1. Structure of the Z Crystal Oscillator The Z crystal oscillator is a resonator made of the piezoelectric effect of the Z crystal (silicon dioxide crystal). Its basic structure is roughly as follows: slice (a wafer for short, it can be a square, a rectangle, or a circle) from a Z crystal at a certain azimuth angle. The silver layer is coated on the two corresponding surfaces as the electrode, weld each lead on each electrode to a pin. In addition, the encapsulation housing constitutes a Z crystal resonator, referred to as Z crystal or crystal, crystal oscillator. Its products are generally encapsulated in metal casings and can also be encapsulated in glass, ceramic, or plastic. It is a Z crystal structure encapsulated in a metal shell. 2. piezoelectric effect If an electric field is added to the two electrodes of the Z crystal, the chip will produce mechanical deformation. If the mechanical pressure is applied on both sides of the wafer, an electric field is generated in the corresponding direction of the wafer. This physical phenomenon is called piezoelectric effect. If an Alternating Voltage is added to the two poles of the chip, the chip will produce mechanical vibration, and the mechanical vibration of the chip will generate an alternating electric field. In general, the amplitude of the mechanical vibration of the wafer and the amplitude of the alternating electric field are very small, but when the frequency of the applied alternating voltage is a specific value, the amplitude increases significantly, it is much larger than the amplitude of other frequencies. This phenomenon is called piezoelectric resonance, which is very similar to the resonance of LC loop. Its resonance frequency is related to the chip cutting method, geometric shape, size, and so on. 3. Symbols and Equivalent Circuits The symbol and equivalent circuit 2 of the Z crystal resonator are shown. When the crystal does not vibrate, it can be regarded as a flat capacitor called electrostatic capacitor C. Its size is related to the chip's geometric size and electrode area, generally about several pf to dozens of PF. When the crystal oscillates, the inertia of mechanical vibration can be equivalent to inductance L. Generally, the L value is dozens of MH. To several hundred MH. The flexibility of the chip can be equivalent to the capacitance C. The value of C is very small, generally only 0.0002 ~ 0.1pf. The loss caused by friction During wafer vibration is equivalent to R, and its value is about 100 Ω. Because the chip has a large equivalent inductance, C is very small, and R is also small, the quality factor Q of the loop is very large, up to 1000 ~ 10000. In addition, the resonance frequency of the wafer is basically only related to the cutting method, geometric shape and size of the wafer, and can be accurate, therefore, a high frequency stability can be obtained by using an oscillating circuit composed of a Z resonator. 4. resonance frequency It can be seen from the equivalent circuit of the Z Crystal Resonator that there are two resonance frequencies, that is, (1) when the branch of L, C, and R series resonance occurs, it has the least equivalent impedance (equal to R ). The resonant frequency in series is expressed by fs. Z crystals have pure resistance to the resonant frequency fs in series. (2) when the frequency is higher than FS, the branches of L, C, and R are sensitive, it can be associated with capacitor C. The parallel resonance occurs, and its parallel frequency is represented by FD. According to the equivalent circuit of the Z crystal, the impedance-frequency characteristic curve 2E can be qualitatively drawn. It can be seen that when the frequency is lower than the series resonance frequency fs or the frequency is higher than the parallel resonance frequency FD, The Z crystal is capacitive. Only within the very narrow range of FS <F <FD, The Z crystal is sensitive. Ii. Characteristics of Z Crystal Oscillator The Z crystal oscillator is a high-quality Z crystal oscillator (consisting of a resonator and an oscillating circuit. The quality, cutting orientation, structure and circuit form of the crystal vibrator determine the performance of the oscillator. The International Electrotechnical Commission (IEC) classifies Z crystal oscillator into four categories: tcxo, vcxo, and tcxo ), constant Temperature Controlled Crystal Oscillator (ocxo ). At present, the development of digital compensated crystal loss oscillator (dcxo) and so on. Common crystal oscillator (spxo) can generate 10 ^ (-5 )~ 10 ^ (-4) magnitude frequency accuracy, standard frequency 1-100 MHz, frequency stability is ± 100ppm. Spxo does not adopt any temperature-frequency compensation measures, which are cheap and usually used as a microprocessor clock device. The package size ranges from 21x14 x 6mm and 5x3.2x1.5. The precision of the Voltage-Controlled Crystal Oscillator (vcxo) is 10 ^ (-6 )~ 10 ^ (-5) magnitude, frequency range: 1 ~ 30 MHz. The frequency stability of a Low-tolerance oscillator is ± 50ppm. It is usually used in the Phase-Locked Loop. Encapsulation size: 14x10x3mm. Temperature compensated crystal oscillator (tcxo) uses temperature sensitive devices for temperature frequency compensation. The frequency accuracy reaches 10 ^ (-7 )~ 10 ^ (-6) magnitude, frequency range: 1-60 MHz, frequency stability: ± 1 ~ ± 2. 5ppm, encapsulation size from 30x30 x 15mm to 11.4x9.6x3.9mm. It is usually used for handheld phones, cellular phones, and two-way wireless communication devices. The constant temperature control crystal oscillator (ocxo) places the crystal and oscillator circuit in the constant temperature box to eliminate the effect of ambient temperature changes on the frequency. The ocxo frequency precision ranges from 10 ^ (-10) to 10 ^ (-8), which is even higher for some special applications. The frequency stability is the highest among the four types of oscillator. Iii. main parameters of the Z Crystal Oscillator The main parameters of the crystal oscillator include nominal frequency, load capacitance, frequency precision, and frequency stability. The nominal frequencies vary depending on the crystal oscillator housing. For example, the nominal frequencies of common crystal oscillator are 48 khz and 500 KHz, 503.5 kHz, 1 MHz ~ 40.50 MHz, etc. For special requirements, the crystal oscillator frequency can reach 1000 There are also some non-nominal frequencies above MHz, such as CRB, ztb, and JA series. The load capacitor is the sum of all the valid capacitors inside and outside the IC block connected by the two leads of the crystal oscillator. It can be seen as a Serial Capacitor connected to the crystal chip in the circuit. Different Load frequencies determine different oscillator frequencies. The load capacitance is not necessarily the same for Crystal Oscillator with the same nominal frequency. Because the Z crystal oscillator has two resonant frequencies, one is a low-load capacitive crystal oscillator that is connected in series with a vibrating crystal oscillator, and the other is a high-load capacitive crystal oscillator that is connected with a resonant crystal oscillator. Therefore, the load capacitor must also be required when the crystal oscillator with the same nominal frequency is exchanged, so it cannot be exchanged rashly. Otherwise, the electrical appliance may not work properly. Frequency accuracy and Frequency Stability: because the performance of common crystal oscillator can basically meet the requirements of General electrical appliances, a certain degree of frequency accuracy and frequency stability are required for high-end equipment. The frequency precision ranges from 10 ^ (-4) to 10 ^ (-10. Stability ranges from ± 1 to ± 100ppm. This should be based on the specific device needs to select appropriate crystal oscillator, such as communications networks, wireless data transmission and other systems need higher requirements of the Z crystal oscillator. Therefore, the crystal oscillator parameters determine the quality and performance of the crystal oscillator. In practical application, you need to select an appropriate crystal oscillator according to specific requirements. because the price of the crystal oscillator varies with performance, the higher the requirement, the more expensive it is. Generally, you only need to meet the requirements. Iv. Development Trend of Z Crystal Oscillator 1. miniaturization, slicing, and slicing: To meet the lightweight, thin, and short requirements of portable products represented by mobile phones, the encapsulation of A Z crystal oscillator is changed from a traditional bare metal shell coated with plastic metal to a ceramic package. For example, the size of devices such as tcxo is reduced by 30 ~ 100 times. The thickness of tcxo in SMD Package is less than 2mm. Currently, 5 x 3mm devices are available. 2. high precision and high stability. At present, the total precision of non-compensated crystal oscillator can reach ± 25ppm, and the frequency stability of vcxo is 10 ~ Generally, the value range is ± 20 to 7 ℃ ~ 100ppm, while the frequency stability of ocxo in the same temperature range is generally ± 0. 0001 ~ 5ppm, vcxo is controlled below ± 25ppm. 3. Low Noise and high frequency. Frequency trembling is not allowed in GPS communication systems. phase noise is an important parameter to characterize oscillator frequency trembling. Currently, the phase noise performance of mainstream ocxo products has been greatly improved. Except vcxo, the maximum output frequency of other types of crystal oscillator shall not exceed 200 MHz. For example, the frequency of the ucv4 series voltage controlled oscillator for GSM and other mobile phones is 650 ~ 1700 MHz, power supply voltage 2.2 ~ 3.3 V, working current 8 ~ 10mA. 4. Low function, fast start, low voltage operation, low level drive and low current consumption have become a trend. Generally, the power supply voltage is 3.3 V. Currently, many tcxo and vcxo products have a current loss of no more than 2. Ma. The Quick Start Technology of the Z crystal oscillator has also made breakthroughs. For example, the VG-2320SC vcxo produced by Seiko in Japan, in the range of ± 0. 1ppm, the frequency stable time is less than 4 ms. SMD produced by Tokyo ceramics Corporation Tcxo can reach 90% of the rated value after 4 ms of oscillating startup. Oak 10 ~ For 25 MHz ocxo products, the stability of ± 0. 01 ppm can be achieved after 5 minutes of pushing. V. Application of Z Crystal Oscillator 1. When the time is accurate, the power consumption is low, and the durability is the biggest advantage. Both the old-fashioned and new-style multi-functional Z clocks use the Z crystal oscillator as the core circuit, and its frequency accuracy determines the walking precision of the electronic clock. The principle of the Z crystal oscillator is shown in Figure 3. V1 and V2 constitute the oscillator system of the CMOS inverter Z crystal Q and the oscillating capacitor C1 and the fine-tuning capacitor C2. Here the Z crystal is equivalent to the inductor. The component parameters of the oscillator system determine the vibration frequency. Generally, Q, C1, and c2 are external components. In addition, R1 is the Feedback resistance, R2 is the stable oscillating resistance, and they are all integrated into the circuit. Therefore, you cannot adjust the travel precision by changing the values of C1 or C2. However, we can still add a capacitor C to change the parameters of the oscillating system to adjust the travel time precision. According to the walking speed of the electronic clock, there are two ways to adjust the capacitance: If the walking speed is fast, the capacitor C, 4 can be connected at both ends of the Z crystal. At this time, the total capacitance of the system increases, the oscillation frequency decreases, and the travel time slows down. If the travel time is slow, the capacitor C can be connected in the crystal branch. 5. At this time, the total capacitance of the system is reduced, the oscillation frequency increases, and the travel time increases rapidly. You can adjust the travel time accuracy after patient and repeated tests. Therefore, the crystal oscillator can be used for clock signal generators. 2. With the development of TV technology, most color TVs have recently adopted crystal oscillator of 503 kHz or 1/3 kHz as the source of the line and Field Circuit oscillator. The stability and reliability of the line frequency of 15625hz are greatly improved. Surface and crystal oscillator are cheap and easy to replace. 3. In the communication system products, the value of the Z crystal oscillator has been more widely reflected, and it has also been developed faster. Many high-performance Z crystals are mainly used in communication networks, wireless data transmission, and high-speed digital data transmission.