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Detail the important indicators of crystal oscillator
Release time:2025/3/26 14:52:58
Crystal oscillator index
Total frequency difference: Let's first understand what is frequency difference, the so-called frequency difference is shorthand for frequency deviation, which is caused by the specified working parameters and non-working parameters in the specified time, resulting in the frequency deviation of the crystal oscillator. The frequency of any crystal oscillator is not absolute, such as our common 12M crystal oscillator, 8M crystal oscillator, 32M crystal oscillator, etc., they are caused by temperature stability, frequency aging rate, frequency voltage characteristics and frequency load characteristics, and finally affect the deviation of the frequency, called the total frequency difference.
Frequency aging rate: The relationship between oscillator frequency and time when the oscillator frequency is measured under constant environmental conditions. This long-term frequency drift is caused by the slow change of crystal components and oscillator circuit components, so the rate of frequency shift is called the aging rate, which can be used after the maximum change rate of the specified time limit (such as ±10ppb/ day, 72 hours after charging), or the maximum total frequency change within the specified time limit (such as: ±1ppm/ (first year) and ±5ppm/ (decade)).
The factors that determine the aging of crystals are:
Molecules of pollutants and residual gases will be deposited on the wafer or oxidize the crystal electrode. The higher the oscillation frequency of the crystal, the thinner the chip used, and the more severe the effect. This effect can be gradually stabilized over a long period of time, and this stability will be repeated with changes in temperature or working state - allowing pollutants to reconcentrate or disperse on the crystal surface
When the crystal oscillator is deformed due to external causes (force, humidity, temperature field changes, etc.), the internal force between the various parts of the object interacts with each other to resist the effect of this external cause, and tries to make the object recover from the position after deformation to the position before deformation stress can be stabilized after a period of change, which is called stress. A crystal cutting method called "stress compensation" (SC cutting method) makes the crystal have better characteristics.
③ Structural process defects, etc.
Therefore, the crystal vibration with low frequency is better than the crystal vibration with high frequency, the crystal vibration with long working time is better than the crystal vibration with short working time, and the crystal vibration with continuous working is better than the crystal vibration with intermittent working time.
Frequency temperature stability: under nominal power supply and load, operating in the specified temperature range without hidden reference temperature or with hidden reference temperature maximum allowable frequency deviation.
ft=±(fmax-fmin)/(fmax+fmin)
ftref = ±MAX[| (fmax-fref)/fref |, | (fmin-fref)/fref |]
ft: Frequency temperature stability (without implied reference temperature)
ftref: Frequency temperature stability (with implied reference temperature)
fmax: The highest frequency measured within a specified temperature range
fmin: The lowest frequency measured within a specified temperature range
fref: Specifies the frequency at which the reference temperature is measured
Note: The crystal oscillator with ftref index is more difficult to produce than the crystal oscillator with ft index, so the crystal oscillator with ftref index is sold at a higher price.
Power-on characteristic (frequency stable preheating time) : refers to the rate of change from the frequency of a period of time after power-on (such as 5 minutes) to the frequency of another period of time after power-on (such as 1 hour). The speed at which the crystal oscillator reaches stability is indicated. This indicator is useful for frequently switched instruments such as frequency meters.
Note: In most applications, the crystal oscillator is powered on for a long time, however in some applications the crystal oscillator needs to be turned on and off frequently, then the frequency stable warm-up time indicator needs to be taken into account (especially for military communication stations used in harsh environments, when it is necessary to
To find the frequency temperature stability ≤±0.3ppm(-45℃ ~ 85℃), using OCXO as the local oscillator, the frequency stability preheating time will be no less than 5 minutes, and using MCXO only takes ten seconds).
Frequency voltage control range: The frequency control voltage is adjusted from the reference voltage to the specified end voltage, the minimum peak change in the crystal oscillator frequency.
Description: The reference voltage is +2.5V, the specified end voltage is +0.5V and +4.5V, and the frequency change of the VCO is -2ppm when the voltage is controlled at the +0.5V frequency, and the frequency is +4.5V
When the frequency change of the control voltage is +2.1ppm, the voltage control range of the VCXO voltage control frequency is expressed as ≥±2ppm(2.5V±2V), the slope is positive, and the linearity is +2.4%.
Voltage frequency response range: The relationship between the peak frequency offset and the modulation frequency when the modulation frequency changes. It is usually expressed that the specified modulation frequency is several dB lower than the specified modulation reference frequency.
Note: VCXO frequency voltage control range frequency response is 0 ~ 10kHz.
Frequency-voltage-controlled linearity: A measure of the transmission characteristics of the output frequency-input control voltage compared to an ideal (linear) function, expressed as a percentage of the admissible nonlinearity of the frequency offset over the entire range.
Note: Typical VCXO frequency voltage control linearity is: ≤±10%, ≤±20%. The simple VCXO frequency voltage-controlled linear calculation method is as follows (when the frequency voltage-controlled polarity is positive) :
Frequency voltage control linearity = ±((fmax-fmin)/ f0)×100%
fmax: Output frequency of the VCXO at the maximum voltage control voltage
fmin: output frequency of the VCXO at the minimum voltage control voltage
f0: voltage frequency of the voltage control center
Single sideband phase noise ￡(f) : The ratio of the power density of a phase modulated sideband to the power of the carrier at departure from carrier f.
Output waveform: In terms of broad categories, the output waveform can be divided into two categories: square wave and sine wave.
Square wave is mainly used in digital communication system clock, the other wave mainly has output level, duty cycle, rise/fall time, drive ability and other indicators.
With the rapid development of science and technology, high quality signal source is needed as carrier of increasingly complex baseband information in communication, radar and high-speed data transmission systems. Because a carrier signal with parasitic amplitude modulation and phase modulation (no
After the clean signal is modulated by the baseband signal containing information, these spectral components that should not exist in the ideal state (parasitic modulation in the carrier) will cause the quality of the transmitted signal and the bit error rate of data transmission to be significantly worse. So as
The carrier of the transmitted signal, the cleanliness of the carrier signal (spectrum purity) has a direct impact on the quality of communication. For sine waves, it is usually necessary to provide indicators such as harmonics, noise, and output power.
Total frequency difference: Let's first understand what is frequency difference, the so-called frequency difference is shorthand for frequency deviation, which is caused by the specified working parameters and non-working parameters in the specified time, resulting in the frequency deviation of the crystal oscillator. The frequency of any crystal oscillator is not absolute, such as our common 12M crystal oscillator, 8M crystal oscillator, 32M crystal oscillator, etc., they are caused by temperature stability, frequency aging rate, frequency voltage characteristics and frequency load characteristics, and finally affect the deviation of the frequency, called the total frequency difference.
Frequency aging rate: The relationship between oscillator frequency and time when the oscillator frequency is measured under constant environmental conditions. This long-term frequency drift is caused by the slow change of crystal components and oscillator circuit components, so the rate of frequency shift is called the aging rate, which can be used after the maximum change rate of the specified time limit (such as ±10ppb/ day, 72 hours after charging), or the maximum total frequency change within the specified time limit (such as: ±1ppm/ (first year) and ±5ppm/ (decade)).
The factors that determine the aging of crystals are:
Molecules of pollutants and residual gases will be deposited on the wafer or oxidize the crystal electrode. The higher the oscillation frequency of the crystal, the thinner the chip used, and the more severe the effect. This effect can be gradually stabilized over a long period of time, and this stability will be repeated with changes in temperature or working state - allowing pollutants to reconcentrate or disperse on the crystal surface
When the crystal oscillator is deformed due to external causes (force, humidity, temperature field changes, etc.), the internal force between the various parts of the object interacts with each other to resist the effect of this external cause, and tries to make the object recover from the position after deformation to the position before deformation stress can be stabilized after a period of change, which is called stress. A crystal cutting method called "stress compensation" (SC cutting method) makes the crystal have better characteristics.
③ Structural process defects, etc.
Therefore, the crystal vibration with low frequency is better than the crystal vibration with high frequency, the crystal vibration with long working time is better than the crystal vibration with short working time, and the crystal vibration with continuous working is better than the crystal vibration with intermittent working time.
Frequency temperature stability: under nominal power supply and load, operating in the specified temperature range without hidden reference temperature or with hidden reference temperature maximum allowable frequency deviation.
ft=±(fmax-fmin)/(fmax+fmin)
ftref = ±MAX[| (fmax-fref)/fref |, | (fmin-fref)/fref |]
ft: Frequency temperature stability (without implied reference temperature)
ftref: Frequency temperature stability (with implied reference temperature)
fmax: The highest frequency measured within a specified temperature range
fmin: The lowest frequency measured within a specified temperature range
fref: Specifies the frequency at which the reference temperature is measured
Note: The crystal oscillator with ftref index is more difficult to produce than the crystal oscillator with ft index, so the crystal oscillator with ftref index is sold at a higher price.
Power-on characteristic (frequency stable preheating time) : refers to the rate of change from the frequency of a period of time after power-on (such as 5 minutes) to the frequency of another period of time after power-on (such as 1 hour). The speed at which the crystal oscillator reaches stability is indicated. This indicator is useful for frequently switched instruments such as frequency meters.
Note: In most applications, the crystal oscillator is powered on for a long time, however in some applications the crystal oscillator needs to be turned on and off frequently, then the frequency stable warm-up time indicator needs to be taken into account (especially for military communication stations used in harsh environments, when it is necessary to
To find the frequency temperature stability ≤±0.3ppm(-45℃ ~ 85℃), using OCXO as the local oscillator, the frequency stability preheating time will be no less than 5 minutes, and using MCXO only takes ten seconds).
Frequency voltage control range: The frequency control voltage is adjusted from the reference voltage to the specified end voltage, the minimum peak change in the crystal oscillator frequency.
Description: The reference voltage is +2.5V, the specified end voltage is +0.5V and +4.5V, and the frequency change of the VCO is -2ppm when the voltage is controlled at the +0.5V frequency, and the frequency is +4.5V
When the frequency change of the control voltage is +2.1ppm, the voltage control range of the VCXO voltage control frequency is expressed as ≥±2ppm(2.5V±2V), the slope is positive, and the linearity is +2.4%.
Voltage frequency response range: The relationship between the peak frequency offset and the modulation frequency when the modulation frequency changes. It is usually expressed that the specified modulation frequency is several dB lower than the specified modulation reference frequency.
Note: VCXO frequency voltage control range frequency response is 0 ~ 10kHz.
Frequency-voltage-controlled linearity: A measure of the transmission characteristics of the output frequency-input control voltage compared to an ideal (linear) function, expressed as a percentage of the admissible nonlinearity of the frequency offset over the entire range.
Note: Typical VCXO frequency voltage control linearity is: ≤±10%, ≤±20%. The simple VCXO frequency voltage-controlled linear calculation method is as follows (when the frequency voltage-controlled polarity is positive) :
Frequency voltage control linearity = ±((fmax-fmin)/ f0)×100%
fmax: Output frequency of the VCXO at the maximum voltage control voltage
fmin: output frequency of the VCXO at the minimum voltage control voltage
f0: voltage frequency of the voltage control center
Single sideband phase noise ￡(f) : The ratio of the power density of a phase modulated sideband to the power of the carrier at departure from carrier f.
Output waveform: In terms of broad categories, the output waveform can be divided into two categories: square wave and sine wave.
Square wave is mainly used in digital communication system clock, the other wave mainly has output level, duty cycle, rise/fall time, drive ability and other indicators.
With the rapid development of science and technology, high quality signal source is needed as carrier of increasingly complex baseband information in communication, radar and high-speed data transmission systems. Because a carrier signal with parasitic amplitude modulation and phase modulation (no
After the clean signal is modulated by the baseband signal containing information, these spectral components that should not exist in the ideal state (parasitic modulation in the carrier) will cause the quality of the transmitted signal and the bit error rate of data transmission to be significantly worse. So as
The carrier of the transmitted signal, the cleanliness of the carrier signal (spectrum purity) has a direct impact on the quality of communication. For sine waves, it is usually necessary to provide indicators such as harmonics, noise, and output power.
