How to Choose Between Active and Passive Crystal Oscillators?
The widespread application of digital technology has driven the increasing demand for quartz crystal oscillators. The original practice of building one or two quartz components into electronic devices is no longer sufficient to meet system requirements. This also reflects the development of crystal oscillator products. Influenced by the development of mobile communication, GPS equipment, instruments, and consumer electronics, miniaturization, surface mount technology, low noise, high frequency accuracy, high stability, and high frequency are important development issues facing quartz crystal oscillators now and in the future. So how do you distinguish between active and passive crystal oscillators? And why are active crystal oscillators better than passive crystal oscillators? Below, the crystal oscillator marketplace will guide you through understanding the selection of crystal oscillator products.
Passive Crystal Oscillators: Passive crystals require the oscillator within a DSP chip. The datasheet provides recommended connection methods. Passive crystals have no voltage input; their signal level is variable, meaning it's determined by the oscillation circuit. The same crystal can be used with various voltages and can be applied to DSPs with different clock signal voltage requirements. Therefore, for general applications, if conditions permit, it's recommended to use a passive crystal, especially suitable for manufacturers with extensive product lines and high-volume production. The disadvantage of passive crystals compared to crystal oscillators is their poorer signal quality. They typically require precise matching of external capacitors, and the surrounding configuration circuitry needs corresponding adjustments when changing to crystals of different frequencies. It's also recommended to use high-precision quartz crystals and avoid using low-precision ceramic crystals whenever possible.
Active crystal oscillators: Active crystal oscillators do not require the DSP's internal oscillator. They offer good signal quality, are relatively stable, and have a simpler connection method, requiring no complex configuration circuitry. The typical usage of an active crystal oscillator is: pin 1 floating, pin 2 grounded, pin 3 connected to the output, and pin 4 connected to the voltage. Compared to passive crystals, the disadvantage of active crystal oscillators is that their signal level is fixed, requiring careful selection of the appropriate output level, resulting in less flexibility, and they are also more expensive. For high-end products, I personally believe that active crystal oscillators are better because they allow for the selection of more precise crystals, even high-end TCXO temperature-compensated crystal oscillators and OCXO temperature-controlled crystal oscillators. Some DSPs lack internal oscillation circuits and can only use active crystal oscillators. Technical indicators affecting crystal oscillator performance include total frequency drift, frequency stabilization warm-up time, frequency aging rate, and voltage control range. Understanding the meaning of these indicators is crucial.
Total Frequency Drift: The maximum frequency difference between the crystal oscillator frequency and the given nominal frequency caused by all specified combinations of operating and non-operating parameters within a specified time period.
Frequency Stabilization Warm-up Time: The time required for the output frequency to fall below the specified frequency tolerance after power-on, based on the crystal oscillator's stable output frequency.
Frequency Aging Rate: The relationship between oscillator frequency and time when measured under constant environmental conditions. This long-term frequency drift is caused by slow changes in the crystal element and oscillator circuit components, and can be expressed as the maximum rate of change after a specified time limit, or the maximum total frequency change within a specified time limit.
Frequency control voltage range: The minimum peak value change in the crystal oscillator frequency when the frequency control voltage is adjusted from the reference voltage to the specified endpoint voltage.
Voltage-controlled frequency response range: The relationship between the peak frequency deviation and the modulation frequency when the modulation frequency changes. It is usually expressed as a specified modulation frequency being a certain dB lower than the specified modulation reference frequency.
Passive Crystal Oscillators: Passive crystals require the oscillator within a DSP chip. The datasheet provides recommended connection methods. Passive crystals have no voltage input; their signal level is variable, meaning it's determined by the oscillation circuit. The same crystal can be used with various voltages and can be applied to DSPs with different clock signal voltage requirements. Therefore, for general applications, if conditions permit, it's recommended to use a passive crystal, especially suitable for manufacturers with extensive product lines and high-volume production. The disadvantage of passive crystals compared to crystal oscillators is their poorer signal quality. They typically require precise matching of external capacitors, and the surrounding configuration circuitry needs corresponding adjustments when changing to crystals of different frequencies. It's also recommended to use high-precision quartz crystals and avoid using low-precision ceramic crystals whenever possible.
Active crystal oscillators: Active crystal oscillators do not require the DSP's internal oscillator. They offer good signal quality, are relatively stable, and have a simpler connection method, requiring no complex configuration circuitry. The typical usage of an active crystal oscillator is: pin 1 floating, pin 2 grounded, pin 3 connected to the output, and pin 4 connected to the voltage. Compared to passive crystals, the disadvantage of active crystal oscillators is that their signal level is fixed, requiring careful selection of the appropriate output level, resulting in less flexibility, and they are also more expensive. For high-end products, I personally believe that active crystal oscillators are better because they allow for the selection of more precise crystals, even high-end TCXO temperature-compensated crystal oscillators and OCXO temperature-controlled crystal oscillators. Some DSPs lack internal oscillation circuits and can only use active crystal oscillators. Technical indicators affecting crystal oscillator performance include total frequency drift, frequency stabilization warm-up time, frequency aging rate, and voltage control range. Understanding the meaning of these indicators is crucial.
Total Frequency Drift: The maximum frequency difference between the crystal oscillator frequency and the given nominal frequency caused by all specified combinations of operating and non-operating parameters within a specified time period.
Frequency Stabilization Warm-up Time: The time required for the output frequency to fall below the specified frequency tolerance after power-on, based on the crystal oscillator's stable output frequency.
Frequency Aging Rate: The relationship between oscillator frequency and time when measured under constant environmental conditions. This long-term frequency drift is caused by slow changes in the crystal element and oscillator circuit components, and can be expressed as the maximum rate of change after a specified time limit, or the maximum total frequency change within a specified time limit.
Frequency control voltage range: The minimum peak value change in the crystal oscillator frequency when the frequency control voltage is adjusted from the reference voltage to the specified endpoint voltage.
Voltage-controlled frequency response range: The relationship between the peak frequency deviation and the modulation frequency when the modulation frequency changes. It is usually expressed as a specified modulation frequency being a certain dB lower than the specified modulation reference frequency.
Mar 13,2026