The crystal oscillator is called the crystal oscillator (English crystal oscillators). Its function is to generate the original clock frequency. This frequency, after the crystal oscillator is amplified or reduced by the frequency generator, becomes a variety of bus frequencies in the computer. Crystal oscillator has different requirements and features, divided into the following categories: ordinary crystal, temperature compensation crystal oscillator, voltage controlled crystal oscillator, temperature controlled crystal oscillator and so on.
Crystals work in a resonant state with a crystal that converts electrical energy and mechanical energy to provide stable, accurate single-frequency oscillations. Under normal operating conditions, the absolute accuracy of ordinary crystal frequencies can reach 50 parts per million. Advanced precision is higher. Some crystal oscillators can also adjust the frequency within a certain range by an applied voltage, called a voltage controlled oscillator (VCO).
The role of the crystal oscillator is to provide the system with a basic clock signal. Usually a system uses a crystal to facilitate the synchronization of the parts. Some communication systems use different crystals for the fundamental frequency and radio frequency, and they keep pace by adjusting the frequency electronically.
Crystals are often used with phase-locked loop circuits to provide the system's desired clock frequency. If different subsystems require clock signals of different frequencies, they can be provided using different PLLs connected to the same crystal.
The DC power supply provided for testing and use should have no ripple content sufficient to affect its accuracy. The AC voltage should be free of transients. The test equipment should have sufficient accuracy and the connections should be reasonably arranged so as to minimize the influence of the test and peripheral circuits on the crystal oscillator.
With some parameters in mind, the design engineer can choose the oscillator for the application.
Countless electronic circuits and applications today require precise timing or clock reference signals. The crystal clock oscillator is well suited for many applications in this area.
The clock oscillator is available in a variety of packages and is characterized by a wide variety of electrical performance specifications. There are several different types: VCXO, TCXO, OCXO, and DCXO. Each type has its own unique properties.
Frequency stability considerations One of the main characteristics of a crystal oscillator is its stability over operating temperature, which is an important factor in determining the oscillator's price. The higher the stability or the wider the temperature range, the higher the price of the device.
The design engineer must carefully determine the actual need for a particular application and then specify the stability of the oscillator. A high index means more money.
For applications requiring ±20ppm frequency stability or more, use an ordinary uncompensated crystal oscillator. TCXO should be considered for stability levels of ±1 to ±20 ppm. For stability below ±1ppm, OCXO or DCXO should be considered.
Other parameters that must be considered for output are output type, phase noise, jitter, voltage stability, load stability, power consumption, package form, shock and vibration, and electromagnetic interference (EMI). The crystal oscillator is HCMOS/TTL compatible, ACMOS compatible, ECL and sine wave output. Each output type has its unique waveform characteristics and uses. Attention should be paid to the requirements of tri-state or complementary outputs. Symmetry, rise and fall times, and logic levels also make provision for certain applications. Many DSPs
And communication chipsets often require strict symmetry (45% to 55%) and fast rise and fall times (less than 5ns).
Phase noise and jitter The phase noise obtained in the frequency domain measurement is a true measure of short-term stability. It can measure up to 1Hz of the center frequency and usually measure 1MHz.
The phase noise of the oscillator improves at frequencies far from the center frequency. The TCXO and OCXO oscillators and other crystal oscillators using fundamental or harmonic modes have the best phase noise performance. Oscillators that use the phase-locked loop synthesizer to produce the output frequency typically exhibit poor phase noise performance over those that use non-phase-locked loop technology.
Jitter is related to phase noise, but it is measured in the time domain. The jitter in picoseconds can be measured with rms or peak-to-peak values. Many applications, such as communications networks, wireless data transmission, ATM, and SONET requirements must meet strict churn specifications. Careful attention is paid to the jitter and phase noise characteristics of the oscillators used in these systems.
Power Supply and Load Effects The frequency stability of the oscillator is also affected by oscillator supply voltage variations and oscillator load changes. Choosing the right oscillator minimizes these effects. Designers should verify oscillator performance under recommended supply voltage tolerances and loads. It cannot be expected that only oscillators rated at 15pF will perform well at 50pF. Oscillators operating above the recommended supply voltage also exhibit bad waveforms and stability.
For devices that require battery power, we must consider the power consumption. The introduction of 3.3V products will inevitably require the development of an oscillator operating at 3.3V. A lower voltage allows the product to operate at low power. Most of today's commercially available surface mount oscillators operate at 3.3V. Many punched oscillators using traditional 5V devices are being redesigned to work at 3.3V.
Similar to other electronic components, the clock oscillator also uses increasingly smaller packages. For example, M-tron's M3L/M5L series of surface mount oscillators are now available in a 3.2 x 5.0 x 1.0mm package. In general, smaller devices are more expensive than larger surface-mount or through-hole devices. Small packages often have a trade-off between performance, output choice, and frequency choice.
The environment in which the working environment oscillator actually applies needs careful consideration. For example, high levels of vibration or shock can cause problems with the oscillator.
In addition to possible physical damage, vibrations or shocks can cause erroneous actions at certain frequencies. These externally induced disturbances cause frequency jitter, increased noise components, and intermittent oscillator failure. ----For EMI-compliant applications, EMI is another priority. In addition to using the proper PC motherboard layout technology, it is important to choose a clock oscillator that provides the least amount of radiation. In general, oscillators with slower rise/fall times exhibit better EMI characteristics.
For frequencies below 70MHz, HCMOS type oscillators are recommended. For higher frequencies, an ECL type oscillator can be used. The ECL oscillator usually has the best overall noise suppression. Even at lower frequencies of 10 to 100 MHz, the ECL type is slightly better than other types of oscillators.
Detection The detection of a crystal oscillator can usually only be done with an oscilloscope (which needs to be powered up via a circuit board) or a frequency meter. Multimeters or other testers cannot be measured. If there is no condition or there is no way to judge whether it is good or bad, it can only be replaced. This is also effective. The common faults of the crystal oscillator are: (a) internal leakage; (b) internal open circuit; (c) metamorphic frequency deviation; (d) external capacitor leakage connected to it. From these failures, the VI curve function of the multimeter and the tester should be able to check for faults (C) and (D), but this will depend on the degree of damage.
Summarizing the selection of devices generally leave some margin to ensure product reliability. The use of higher-grade devices can further reduce the probability of failure and bring potential benefits, which should also be taken into account when comparing product prices. To make the oscillator's "overall performance" balanced and reasonable, it is necessary to weigh many factors such as stability, operating temperature range, crystal aging effect, phase noise, and cost. The cost here does not only include the price of the device. And it includes the cost of use for the entire life of the product.
Crystals work in a resonant state with a crystal that converts electrical energy and mechanical energy to provide stable, accurate single-frequency oscillations. Under normal operating conditions, the absolute accuracy of ordinary crystal frequencies can reach 50 parts per million. Advanced precision is higher. Some crystal oscillators can also adjust the frequency within a certain range by an applied voltage, called a voltage controlled oscillator (VCO).
The role of the crystal oscillator is to provide the system with a basic clock signal. Usually a system uses a crystal to facilitate the synchronization of the parts. Some communication systems use different crystals for the fundamental frequency and radio frequency, and they keep pace by adjusting the frequency electronically.
Crystals are often used with phase-locked loop circuits to provide the system's desired clock frequency. If different subsystems require clock signals of different frequencies, they can be provided using different PLLs connected to the same crystal.
The DC power supply provided for testing and use should have no ripple content sufficient to affect its accuracy. The AC voltage should be free of transients. The test equipment should have sufficient accuracy and the connections should be reasonably arranged so as to minimize the influence of the test and peripheral circuits on the crystal oscillator.
With some parameters in mind, the design engineer can choose the oscillator for the application.
Countless electronic circuits and applications today require precise timing or clock reference signals. The crystal clock oscillator is well suited for many applications in this area.
The clock oscillator is available in a variety of packages and is characterized by a wide variety of electrical performance specifications. There are several different types: VCXO, TCXO, OCXO, and DCXO. Each type has its own unique properties.
Frequency stability considerations One of the main characteristics of a crystal oscillator is its stability over operating temperature, which is an important factor in determining the oscillator's price. The higher the stability or the wider the temperature range, the higher the price of the device.
The design engineer must carefully determine the actual need for a particular application and then specify the stability of the oscillator. A high index means more money.
For applications requiring ±20ppm frequency stability or more, use an ordinary uncompensated crystal oscillator. TCXO should be considered for stability levels of ±1 to ±20 ppm. For stability below ±1ppm, OCXO or DCXO should be considered.
Other parameters that must be considered for output are output type, phase noise, jitter, voltage stability, load stability, power consumption, package form, shock and vibration, and electromagnetic interference (EMI). The crystal oscillator is HCMOS/TTL compatible, ACMOS compatible, ECL and sine wave output. Each output type has its unique waveform characteristics and uses. Attention should be paid to the requirements of tri-state or complementary outputs. Symmetry, rise and fall times, and logic levels also make provision for certain applications. Many DSPs
And communication chipsets often require strict symmetry (45% to 55%) and fast rise and fall times (less than 5ns).
Phase noise and jitter The phase noise obtained in the frequency domain measurement is a true measure of short-term stability. It can measure up to 1Hz of the center frequency and usually measure 1MHz.
The phase noise of the oscillator improves at frequencies far from the center frequency. The TCXO and OCXO oscillators and other crystal oscillators using fundamental or harmonic modes have the best phase noise performance. Oscillators that use the phase-locked loop synthesizer to produce the output frequency typically exhibit poor phase noise performance over those that use non-phase-locked loop technology.
Jitter is related to phase noise, but it is measured in the time domain. The jitter in picoseconds can be measured with rms or peak-to-peak values. Many applications, such as communications networks, wireless data transmission, ATM, and SONET requirements must meet strict churn specifications. Careful attention is paid to the jitter and phase noise characteristics of the oscillators used in these systems.
Power Supply and Load Effects The frequency stability of the oscillator is also affected by oscillator supply voltage variations and oscillator load changes. Choosing the right oscillator minimizes these effects. Designers should verify oscillator performance under recommended supply voltage tolerances and loads. It cannot be expected that only oscillators rated at 15pF will perform well at 50pF. Oscillators operating above the recommended supply voltage also exhibit bad waveforms and stability.
For devices that require battery power, we must consider the power consumption. The introduction of 3.3V products will inevitably require the development of an oscillator operating at 3.3V. A lower voltage allows the product to operate at low power. Most of today's commercially available surface mount oscillators operate at 3.3V. Many punched oscillators using traditional 5V devices are being redesigned to work at 3.3V.
Similar to other electronic components, the clock oscillator also uses increasingly smaller packages. For example, M-tron's M3L/M5L series of surface mount oscillators are now available in a 3.2 x 5.0 x 1.0mm package. In general, smaller devices are more expensive than larger surface-mount or through-hole devices. Small packages often have a trade-off between performance, output choice, and frequency choice.
The environment in which the working environment oscillator actually applies needs careful consideration. For example, high levels of vibration or shock can cause problems with the oscillator.
In addition to possible physical damage, vibrations or shocks can cause erroneous actions at certain frequencies. These externally induced disturbances cause frequency jitter, increased noise components, and intermittent oscillator failure. ----For EMI-compliant applications, EMI is another priority. In addition to using the proper PC motherboard layout technology, it is important to choose a clock oscillator that provides the least amount of radiation. In general, oscillators with slower rise/fall times exhibit better EMI characteristics.
For frequencies below 70MHz, HCMOS type oscillators are recommended. For higher frequencies, an ECL type oscillator can be used. The ECL oscillator usually has the best overall noise suppression. Even at lower frequencies of 10 to 100 MHz, the ECL type is slightly better than other types of oscillators.
Detection The detection of a crystal oscillator can usually only be done with an oscilloscope (which needs to be powered up via a circuit board) or a frequency meter. Multimeters or other testers cannot be measured. If there is no condition or there is no way to judge whether it is good or bad, it can only be replaced. This is also effective. The common faults of the crystal oscillator are: (a) internal leakage; (b) internal open circuit; (c) metamorphic frequency deviation; (d) external capacitor leakage connected to it. From these failures, the VI curve function of the multimeter and the tester should be able to check for faults (C) and (D), but this will depend on the degree of damage.
Summarizing the selection of devices generally leave some margin to ensure product reliability. The use of higher-grade devices can further reduce the probability of failure and bring potential benefits, which should also be taken into account when comparing product prices. To make the oscillator's "overall performance" balanced and reasonable, it is necessary to weigh many factors such as stability, operating temperature range, crystal aging effect, phase noise, and cost. The cost here does not only include the price of the device. And it includes the cost of use for the entire life of the product.
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