With the rapid development of information technology, miniaturized products are gaining increasing popularity. The crystal oscillator industry is no exception. Nowadays, more and more electronic devices opt for compact and thin SMD crystal oscillators, gradually narrowing the application scope of through-hole crystal oscillators. Today, let’s talk about how to identify the pin orientation of SMD crystal oscillators.
1. What is an SMD Crystal Oscillator?
The commonly mentioned crystal oscillator is a type of quartz crystal component. Quartz crystal resonators, quartz crystal oscillators and quartz crystal filters all fall into the category of quartz crystal components. Quartz crystal is a piezoelectric crystal. When a piezoelectric crystal is squeezed or stretched in a specific direction, different electric charges will be generated at its two ends. It can be divided into the direct piezoelectric effect and inverse piezoelectric effect based on different working principles.
SMD crystal oscillators are mainly applied to clock modules in circuits to provide clock reference signals. They are widely used in embedded designs, such as FPGA, DSP and other development boards.
2. Similarities and Differences in Pins Between Passive and Active Crystal Oscillators
Common SMD crystal oscillators are mainly classified into two types: passive crystal oscillators and active crystal oscillators. Generally, passive crystal oscillators have no installation direction limitation but are equipped with pins. Many people struggle to distinguish the pins of passive and active crystal oscillators. Here is an easy-to-remember method:
- 2-pin SMD crystal oscillators are always passive.
- 4-pin SMD crystal oscillators can be either passive or active.
- SMD crystal oscillators with 6 pins or more are all active.
3. How to Distinguish the Pin Orientation of SMD Crystal Oscillators
Common SMD crystal oscillator specifications include: 2.5×2.0mm, 3.2×2.5mm, 5.0×3.2mm, 6.0×3.5mm and 5.0×7.0mm.
2-pin passive SMD crystal oscillators are mostly ceramic-surface types, while metal-surface types also exist. Generally, metal-surface crystal oscillators are mostly 4-pin passive models.
It is a common problem to identify the pin definition of 4-pin SMD crystal oscillators. For 4-pin passive crystal oscillators, only two pins are functional, and the other two are floating and do not need circuit connection, defined as Pin 1, Pin 2, Pin 3 and Pin 4 respectively.
Quick Identification Tips
Manufacturers will mark obvious positioning features for easy identification:
- For 4-pin passive SMD crystal oscillators: A notch is marked next to Pin 1. Count clockwise in sequence as Pin 1, Pin 2, Pin 3 and Pin 4. Normally, Pin 1 and Pin 3 are grounded, while Pin 2 and Pin 4 are non-functional floating pins.
- For active crystal oscillators: A dot mark indicates Pin 1. Count pins clockwise on the reverse side to confirm the complete pin sequence.
Active crystal oscillators are further divided into multiple types: quartz oscillators, temperature compensated crystal oscillators (TCXO), voltage controlled oscillators (VCXO), and voltage controlled temperature compensated crystal oscillators (VCTCXO).
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