Yes, the crystals used in oscillators and crystals used in crystal filters are different in terms of design, specifications, and intended function. While both types are made from quartz crystals and rely on the piezoelectric effect, they are optimized for different electrical characteristics to fulfill distinct roles in electronic circuits.
1. Purpose and Function
Aspect
| Crystals for Oscillators
| Crystals for Crystal Filters
|
Primary Function
| Generate a precise, stable frequency
| Filter specific frequency ranges
|
Application
| Used in clock generation, timing, RF sources
| Used in signal processing, RF filtering
|
Electrical Response
| Operates at its fundamental frequency
| Operates at multiple resonant modes or harmonis
|
2. Electrical Characteristics
Characteristic
| Oscillator Crystals
| Crystal Filter Crystals
|
Resonant Frequency
| Single, precise frequency (fundamental)
| Narrow frequency band or multiple modes
|
Load Capacitance (CL)
| Specific CL value for stable oscillation
| Matched to filter circuit requirements
|
Equivalent Series Resistance (ESR)
| Low ESR for high efficiency
| Moderate ESR, tuned for specific filter characteristics
|
Q Factor (Quality Factor)
| Moderate to High (10,000-100,000)
| Very High (up to 1,000,000 for narrow filters)
|
Aging/Drift
| Minimal for long-term stability
| Less critical unless used in precision filters
|
3. Physical Design Differences
Aspect
| Oscillator Crystals
| Crystal Filter Crystals
|
Cut Type
| AT-cut (common) for low temp sensitivity
| AT-cut or specialized filter cuts (like BT-cut)
|
Package Type
| Standard packages like HC-49, SMD, TO-39
| Matched arrays in filter assemblies
|
Mounting Design
| Typically single-element
| May involve multiple crystal elements
|
Crystal Size
| Standard size based on operating frequency
| Custom-sized and precision-matched for bandpass, band-stop filters
|
4. Operating Principles
Oscillator Crystals:
• Mode of Operation:
• Operate at their fundamental frequency or overtone frequencies.
• Designed for stable and continuous frequency generation.
• Example:
• 32.768 kHz Quartz Crystal for real-time clocks.
• 10 MHz OCXO Crystal for RF signal generators.
Crystal Filter Crystals:
• Mode of Operation:
• Operate in resonance and anti-resonance modes to allow specific frequency bands while rejecting others.
• High Q factor ensures sharp frequency selectivity.
• Types of Crystal Filters:
• Band-Pass Filters: Pass only a certain frequency range.
• Band-Stop Filters (Notch Filters): Reject specific frequencies.
• Ladder and Monolithic Filters: Use multiple crystals in precise configurations.
5. Applications
Crystals for Oscillators:
• Frequency Generation in:
• Microcontrollers, clocks, watches
• GPS devices, mobile phones
• RF transmitters and receivers
Crystals for Crystal Filters:
• Frequency Filtering in:
• RF communication receivers (e.g., HF/VHF transceivers)
• Military and aerospace signal processing
• Communication base stations
• Precision test equipment
Conclusion: Key Differences
1. Oscillator Crystals: Designed for frequency generation with stability, low ESR, and moderate Q-factor.
2. Crystal Filter Crystals: Designed for selective filtering with high Q-factor, precise frequency response, and custom packaging for signal filtering applications.
DEI recommend P/N:
HTXTAL5200CA-32.768KHz
XTAL1210AL
XTAL1612AL
DEI5856-455KHz
DEI5751-1.4MHz