"1, crystal (CRYSTAL)
Some RD refer to it is crystal: quartz crystal, is passive two feet, no direction, requires IC or other external crystal oscillator input, only frequency, is no direction. The crystal also needs a reverse device that can make a oscillator. The quartz crystal element is composed of a quartz crystal sheet and a housing, commonly known as crystal, crystal, and my country's early referred to a crystal resonator. It can be seen that the normal quartz crystal element (both feet) is no direction, but it is possible to have direction when an lead-out end (pin) is connected to the outer casing.
Crystal is an electromechanical device that is made of quartz crystals with small electrical losses. The precision cutting grinding and plated with electrode welding. This crystal has a very important feature. If he gives him power, he will generate mechanical oscillations. In turn, if he gives him a mechanical force, he will generate electricity, this feature called electromechanical effect. They have a very important feature that is closely related to their shape, material, cutting direction, and the like. Since quartz crystal chemical performance is very stable, the coefficient of thermal expansion is very small, its oscillation frequency is also very stable, and since the control geometry can be done very precise, its resonant frequency is also very accurate.
- What is the use of the reverse, load capacitor? ? why would?
- Forming positive feedback, so that you can
The resonator and Zhong Zhen have, but the resonator is the simplest oscillator without any compensation, and the Zhong Zhen we usually say is made up of a resonator to form a loop to achieve its own function. Take VCXO as an example: a voltage controlled crystal oscillator (VCXO) is a quartz crystal oscillator that can be variable or modulated by the infrared control voltage. The VCXO is mainly composed of quartz resonator, vane diodes, and oscillator circuits, and its working principle is to change the capacitance of the varactor diode by controlling voltage, thereby "traction" quartz resonator frequency to achieve frequency modulation. VCXO is mostly used for locking technology, frequency negative feedback modulation purposes. And how do you choose how to choose it?
2. Zhong Zhen (Oscillator)
Some RDs also referred to as crystal, generally four feet, have a direction, power supply, ground and clock output pins, crystal and oscillating circuits inside, without input input signal sources, and can generate frequencies directly. The factory frequency has been calibrated. Features: Applicability, frequency stable, less electromagnetic radiation. But the price is more expensive than crystal. The quartz crystal oscillator is referred to as crystal, typically from quartz crystal elements, ICs and sealing and housing, which can output a stable frequency signal. The crystal oscillator is generally 4 foots (leading ends), and there are directionality, samples, or indicia in the specification.
Resonator: The moderate effect in the circuit is a network with a frequency of frequency, which is the core component of the oscillation circuit determines the type of frequency stability of the oscillator: quartz crystal, ceramics, LC, medium The resonator of materials. Quartz crystals and amplifying circuits If they are positively feedback, and the loop amplification factor is greater than one generation of self-excited oscillation signals. This is the basic principle of the quartz transistor.
Select ------ According to the specific requirements of the IC you use, 1) can only use external clocks, select oscillators, or crystal + inverter + capacitance to consume oscillators, take the price and convenient. 2) If the external clock can be used, crystal can also be used, and the crystal oscillator, 3), if only the crystal can be used, crystallize crystal
The difference, application range and usage of passive crystals and active crystals:
1. Passive crystals - passive crystals require an oscillator in the DSP on the Datasheet, there is a suggested connection method. The passive crystal has no voltage, the signal level is variable, that is to say, according to the rocking circuit, the same crystal can be applied to a plurality of voltages, which can be used in a variety of DSPs required by multiple clock signal voltage requirements. And the price is usually low, so if the general application is recommended, it is recommended to use crystals for the conditions, which is especially suitable for producers who have a large mass of the product line.
Passive crystals relative to crystals are poor signal quality, typically need to accurately match peripheral circuits (for signal matching capacitors, inductors, etc.), replace different frequencies crystals, the peripheral configuration circuit needs to be adjusted . It is recommended to adopt quartz crystals with high precision, and do not use low precision ceramics to be vigilant.
2, the active crystal-active crystal does not require the internal oscillator of the DSP, the signal quality is good, relatively stable, and the connection method is relatively simple (mainly for power filtering, usually using a capacitor and inductive PI filter network The output is the resistor filter signal with a small resistance value) and does not require a complex configuration circuit.
Active crystal oscillator usual usage: one foot is suspended, bizard, three-footed output, four foot receiving voltages. Relative to passive crystals, defects of active crystals are fixed, requiring a suitable output level, poor flexibility, and high price.
For timing requirements, sensitive applications, individuals think it is still active crystal, because it can be used to select a relatively precise crystal, even high-grade temperature compensation crystals. Some DSPs have no starting circuits, only active crystals, such as TI 6000 series, etc. Active crystal is usually larger than passive crystals, but now many active crystals are epitomic, volume and crystals, and even more crystals.
Some precautions:
1. The DSP that needs multiplier needs to be configured with the Configuration circuit of the PLL, mainly quarantine and filtering;
The crystal crystals below 2, 20 MHz are basically the baseband device, the stability is good, mostly harmonics (such as 3 harmonics, 5 harmonics, etc.), and strong recommendations Using low-frequency devices, the peripheral configuration required by multiplier PLL circuit is mainly capacitive, resistance, inductance, stability and price aspects of crystal crystal devices;
3, the length of the clock signal line is as short as possible, the line width is as large, and the other printed line spacing is as large as possible, close to the device layout wiring, if necessary, can take the inner layer, and surround the ground;
4. There is a special design requirement when the backplane is introduced from the outside, which requires a detailed reference to the relevant information. In addition, some explanations: Overall, the stability of crystal oscillators is better than crystals, especially precision measurements, and most of them are high-grade crystals, so they can integrate various compensation technologies. Reduce the complexity of the design. Imagine if the crystals are used, then design waveform plastic, anti-interference, temperature compensation, what is the complexity of the design? We design radio frequency circuits such as RF circuits to high clock requirements, which is to use high-precision thermal supplementary crystal, industrial grade to be a few hundred yuan.
Applications of special fields If the appropriate crystal is not found, that is, the complexity of the design is exceeded in the market, and it must be designed. In this case, it is necessary to use crystals, but these crystals are definitely not the market. Ordinary crystals, but special high-end crystals such as ruby crystals, and the like. The higher demand is more special. We use the clocks used in high-precision testing even at the high-precision test, and the dedicated radi-frequency connector is connected, it is a large device, quite cumbersome.
Case: The so-called quartz crystal resonator and quartz crystal clock oscillator are collectively referred to. However, due to more, the resonator is used in the consumer electronics, the crystal is equivalent to the resonator is understood. The latter is usually the ivitated.
---- Total Frequency Difference: In the specified period of time, the maximum frequency of the crystal oscillator frequency and the given nominal frequency due to the predetermined work and all combinations of non-working parameters.
---- Description: The total frequency difference includes the maximum frequency difference caused by frequency temperature stability, frequency temperature accuracy, frequency aging, frequency power supply voltage stability, and frequency load stability. It is generally only used in applications where short-term frequency stability is concerned, and the other frequency stability index is not strictly required. For example: precision lanes.
---- Frequency Temperature Stability: Under nominal power and load, the maximum allowable frequency bias that works without hidden reference temperatures or hidden reference temperatures within the specified temperature range.
---- Ft = ± (fmax-fmin) / (fmax + fmin)
---- FTREF = ± Max [| (fMAX-FREF) / FREF |, | (FMIN-FREF) / FREF |] FT: Frequency Temperature Stability (without implicit reference temperature)
---- FTREF: Frequency Temperature Stability (with hidden reference temperature)
---- FMAX: The highest frequency measured within the temperature range
---- FMIN: the lowest frequency measured within the temperature range
---- FREF: Specifies the frequency measured by the reference temperature
---- Description: The crystal oscillator using the FTRef index is higher than the crystal oscillator using the FT indicator, so the crystal oscillator of the FTREF is high.
---- The typical frequency temperature stability indicator of several crystal oscillators used in several electronic systems is shown in the table:
---- There is a part of the frequency temperature stability index in the table should be a frequency temperature stability index indicator with an implicit reference temperature, but did not expose. (1 ppm = 1 × 10-6; 1 ppb = 1 × 10-9).
---- Frequency Stable Preheating Time: The time required from the power-on to the output frequency is less than the predetermined frequency allowance by the crystal oscillator stabilization output frequency.
---- Instructions: In most applications, crystal oscillators are long-term power, however, crystal oscillators in some applications require frequent booting and shutdown, this time the frequency stable preheating time indicator needs to be considered (especially in particular It is a military communication station used in a harsh environment. When the frequency temperature stability is ≤ ± 0.3ppm (-45 ° C ~ 85 ° C), OCXO is used as the vibration, and the frequency stable preheating time will not be less than 5 minutes. It takes more than ten seconds to use DTCXO).
---- Frequency aging rate: The relationship between the oscillator frequency and the time is measured when the oscillator frequency is measured under a constant environmental conditions. Such long-term frequency drift is caused by the slow change of the crystal element and the oscillator circuit component, and the maximum change in time limit (such as ± 10 ppb / day, 72 hours), or the specified time limit is the largest. Frequency changes (such as ± 1 ppm / (first) and ± 5ppm / (decade)) are expressed.
. Since the frequency change caused by temperature changes will greatly exceed the frequency aging of the temperature compensation crystal oscillator under the conditions of the temperature compensation crystal oscillator, this indicator has lost its actual significance). The frequency aging rate of OCXO is: ± 0.5 ppb ~ ± 10 ppb / day (after 72 hours of power), ± 30ppb ~ ± 2 ppm (first), ± 0.3ppm ~ ± 3 ppm (decade).
---- Frequency voltage control range: The frequency control voltage is adjusted from the reference voltage to the specified endpoint voltage, and the minimum peak change amount of the crystal oscillator frequency is changed.
---- Description: The reference voltage is + 2.5V, the specified endpoint voltage is + 0.5V and + 4.5V, the voltage control crystal oscillator is changed to -110 ppm when the + 0.5V frequency control voltage is -110 ppm, at +45V frequency The frequency change amount is + 130 ppm when the control voltage is controlled, and the VCXO voltage control frequency voltage control range is represented as: ≥ ± 100ppm (2.5V ± 2V). Voltage-control frequency response range: When the modulation frequency changes, the relationship between peak frequency offset and modulation frequency. It is usually represented by a predetermined modulation frequency than a predetermined modulation reference frequency.
---- Description: The VCXO frequency voltage control range frequency response is from 0 to 10 kHz.
---- Frequency voltage control linearity: output frequency - input control voltage transmission characteristics compared to the ideal (straight line) function, which represents the entire range of frequent ranges with a percentage.
---- Description: Typical VCXO frequency voltage control linear is: ≤ ± 10%, ≤ ± 20%. Simple VCXO frequency voltage control linear calculation method is (when the frequency voltage control is polar):
---- Frequency voltage control linear = ± (fmax-fmin) / f0) × 100%
---- FMAX: VCXO output frequency at maximum voltage control voltage
---- FMIN: VCXO output frequency when the minimum voltage control voltage
---- F0: Voltage control center voltage frequency ---- Single-sided band phase noise £ (f): Death of the carrier F, the ratio of the power density of the phase modulation track and the carrier power.
Crystal oscillator overview
First, crystal oscillator type:
1. Ordinary crystal oscillator PackageDcrystaloscillator (PXO) is the simplest and most suitable for which the basic control element is the oscillator of crystal components. It is determined by the crystal components employed because there is no temperature control and temperature compensation mode.
2. Voltage Control Crystal Oscillator VoltageControlledCrystaloscillator (VCXO) is biased or modulated with a crystal oscillator output from which the frequency output is biased or modulated. The frequency-temperature characteristics of VCXO are similar to PXO, which is mainly determined by the crystal components employed.
3, Temperature Compensation Crystal Oscillator TemperatureCompensatedCrystaloscillator (TCXO) includes a digital compensation crystal oscillator (DCXODIGITALLYCOMPENSATEDCRYSTALOSCILLATOR) and a microcomputer compensation crystal oscillator (MCXOMicRoComputercompensatedCrystaloscillator). The device is used inside an analog compensation network or a digital compensation method, and the frequency-temperature characteristics of the crystalline element are compensated by the change of the crystal load electrical anti-temperature to achieve a crystal oscillator that reduces its frequency-temperature offset.
4, the constant temperature control crystal oscillator OvenControlledCrystaloscillator (OCXO) is at least placed in the heat shield (such as a constant temperature groove) to control its temperature so that the crystal temperature is substantially unchanged crystal oscillator.
5. Voltage Control - Warning Crystal Oscillator (VCTCXO) Temperature Compensation Crystal Oscillator and Voltage Control Crystal Oscillator Binding.
6. Voltage control - constant temperature crystal oscillator (VCOCX) constant temperature crystal oscillator and voltage control crystal oscillator binding.
Second, the main parameters of crystal oscillator
★ Frequency accuracy: In nominal power supply voltage, nominal load impedance, reference temperature (252 ° C) and other conditions remain unchanged, the frequency of the crystal oscillator relative to the nominal value of the nominal value is permitted.Poor, ie (fmax-fmin) / f0;
★ Temperature stability: other conditions remain unchanged, the maximum change in the output frequency of the crystal oscillator output in the specified temperature range is allowed to exceed the sum of the sum of the sum of the output frequency extreme value in the temperature range, i.e. (FMAX-FMIN) / FMAX + FMIN);
★ Frequency adjustment range: Change the range of output frequencies by adjusting a variable component of the crystal oscillator. Frequency adjustment is:
1 Adjust the output frequency to a predetermined value within the frequency range;
2 Due to aging or other reasons, the output frequency of the crystal oscillator generates an offset, and the output frequency is adjusted to a predetermined value.
★ FM (voltage control) characteristics: including adjustment frequency offset, frequency frequency sensitivity, frequency band lineage.
1 Adjust frequency off: The output frequency is poor when the voltage controlled crystal oscillator control voltage changes from the nominal maximum to the minimum.
2 FM sensitivity: The amount of output frequency caused by the control voltage caused by voltage controlled crystal oscillator variations.
3 Model linearity: is a measure of the modulation system transmission characteristics compared to the ideal line (minimum multiplier). It is usually expressed in a percentage of deviation from the ideal straight line within a specified range.
★ Load characteristics: Other conditions remain unchanged, and load the maximum allowable frequency offset of the transistor output frequency relative to the nominal load in the specified variation.
★ Voltage characteristics: Other conditions remain unchanged, the maximum allowable frequency of the output frequency of the crystal oscillator output frequency relative to the nominal power supply voltage in the specified change range.
★ Clutter: The discrete spectrum component of the output signal and the main frequency-harmonic (except for sub-harmonics) is represented by the DBC.
★ Harmonic: The ratio of the harmonic component power Pi and the carrier power P0 is represented by DBC.
★ Frequency aging: Under the predetermined environmental conditions, the output frequency caused by the aging of the component (mainly quartz resonators) over time system drift process. It is usually used to measure the frequency difference within a certain time interval. For high stable crystals, since the output frequency is approximately linearly drifting in a longer working time, the aging rate (relative frequency change in unit time) is often measured. Such as: 10-8 / day or 10-6 / year, etc..
★ Daily fluctuation: After the oscillator is specified, measured once every hour, continuous measurement of 24 hours, calculate the test data by S = (FMAX-FMIN) / F0, to get the day fluctuation.
★ Launch Characteristics: The maximum change in the oscillator frequency value is represented by V = (FMAX-FMIN) / F0 in the predetermined preheating time.
★ Phase noise: frequency domain metrics in short-term stability. The ratio of single-sided noise and carrier noise ratio is represented, £ (f) is directly related to the spectral density Sφ (f) of the noise undulation, and the frequency undulating spectral density Sy (f) is represented by the following formula:
F2S (f) = f02sy (f) = 2f2 £ (f)
F-Fourier frequency or deviation of carrier frequencies; how to select crystal crystal oscillator in the F0-carrier frequency
Pay attention to some parameters, design engineers can choose to appropriate oscillators
---- Numerous electronic lines and applications today require precision or clock reference signals. The crystal clock oscillator is extremely suitable for many applications in this.
---- Clock oscillator has a variety of packages, which are characterized by a variety of electrical performance specifications. It has several different types: voltage control crystal oscillator (VCX), temperature compensation crystal oscillator (TCXO), a thermostat crystal oscillator (OCXO), and a digital compensation crystal oscillator (DCXO). Every type has its own uniqueness.
---- The frequency stability considers that one of the main characteristics of the crystal oscillator is the stability within the operating temperature, which is an important factor in determining the price of the oscillator. The higher the stability or the wider temperature range, the higher the price of the device is also higher.
---- Design engineer should be carefully determined to determine the actual needs of a particular application and then specify the stability of the oscillator. The overall indicator means that the more the money is much.
---- For frequency stability requirements of ± 20ppm or more, ordinary non-compensated crystal oscillators can be used. For the stability of ± 1 to ± 20 ppm, TCXO should be considered. For the stability below ± 1 ppm, OCXO or DCXO should be considered.
---- Other parameters required to consider are output type, phase noise, jitter, voltage stability, load stability, power consumption, package form, impact and vibration, and electromagnetic interference (EMI). The crystal can be HCMOS / TTL compatible, ACMOS compatible, ECL and sine wave output. Each output type has its unique waveform characteristics and use. It should be paid to the requirements of tri-state or complementary output. Symmetry, rising and falling time and logic levels must also be specified for some applications. Many DSPs and Communication Chipmas often require strict symmetry (45% to 55%) and fast rising and falling time (less than 5 ns).
---- Phase Noise and Jitter ---- Phase noise obtained in frequency domain measurement is a real measure of short-term stability. It can measure the 1Hz of the central frequency and usually measured to 1 MHz.
---- The phase noise of the oscillator is improved in the frequency of the center frequency. TCXO and OCXO oscillators and other crystal oscillators that utilize fundamental or harmonic methods have the best phase noise performance. An oscillator using a phase-locked loop synthesizer generates an output frequency is generally presented in poor phase noise performance than an oscillator using a non-locked loop technology.
---- Jitter is related to phase noise, but it measures at time domain. The jitter represented by a slight second is available or peak.
- Peak measurement. Many applications, such as communication networks, wireless data transmission, ATM, and SONET requires a strict mixing indicator. Need to pay close attention to the jitter and phase noise characteristics of the oscillator applied in these systems.
---- The impact of power and load ---- The frequency stability of the oscillator is also affected by the vapority of the oscillator and the effect of oscillator load changes. Correctly selecting an oscillator minimizes these effects. Designers should check the performance of the oscillator under the recommended supply voltage tolerance and load. It is not expected that only the oscillator that can only be rated 15PF is active in driving 50pf. Oscillators working under the suggested supply voltage will also present bad waveforms and stability.
---- For devices that require battery powers, we must consider power consumption. The introduction of 3.3V products must develop oscillators working at 3.3V. ---- Lower voltage allows the product to run at low power. Most commercially available surface mount oscillators working at 3.3V. Many perforated oscillators using traditional 5V devices are redesigned to work at 3.3V.
---- The package is similar to other electronic components, and the clock oscillator also uses the increasingly small package. For example, M-Tron's M3L / M5L series surface mount oscillator is now available in a package of 3.2 × 5.0 × 1.0 mm. Typically, smaller devices are more expensive than large surface mounts or perforated packages. Small packages are often compromised between performance, output selection, and frequency selection.
---- Working Environment ---- The environment in which the oscillator actually applies needs to be careful. For example, high vibration or impact levels will bring problems to the oscillator.
---- In addition to possible physical damage, vibration or impact can cause errors in some frequencies. These external sensing disturbances produce frequency beats, increasing noise assemblies, and intermittent oscillator failure. ---- For applications requiring special EMI compatible, EMI is another problem to be prioritized. In addition to adopting a suitable PCB motherboard layout technology, it is important to choose a clock oscillator that provides the smallest radiation. In general, an oscillator having a slowed rising / falling time presents better EMI characteristics.
---- For the frequency of 70MHz or less, it is recommended to use the HCMOS type oscillator. For higher frequencies, an ECL type oscillator can be used. The ECL type oscillator typically has the best total noise suppression, even at a lower frequency of 10 to 100 MHz, and the ECL type is slightly better than other oscillators.
Original link: https://www.eeboard.com/news/crystal/
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