Complete Analysis of Pin Definitions for Four Pin Crystal Oscillators: Core Differences and Identification Techniques Between Active and Passive Crystal Oscillators

In electronic circuits, four pin crystal oscillators are widely used due to their compact packaging and strong adaptability. However, there are significant differences in pin functions between active and passive types, which need to be distinguished based on their internal structure and working logic.

Taijing Technology SPXO/XO-2016 model

1. Four pin active crystal oscillator: functional division of complete oscillator

Active crystal oscillator is an independent signal source that integrates quartz crystal, oscillation circuit, and amplification module. It can output a stable clock without external assistance, and the four pin definition has clear functional directions:

1-pin (NC/OE): Most of them are empty pins (NC), reserved only for packaging design; Some models are output enable terminals (OE), which can control the signal output state through high and low level switching. They are commonly used for clock sleep and wake-up in low-power scenarios.

2-pin (GND): Ground pin, connected to the system ground potential, providing a stable reference for internal circuits while shielding external electromagnetic interference to ensure signal purity.

3-pin (OUT): The clock signal output terminal outputs a fixed frequency square wave or sine wave signal, directly providing timing reference for core chips such as CPU and FPGA, with frequency accuracy up to ± 10ppm.

4-pin (VCC): The power input terminal needs to be connected to the rated voltage (commonly 3.3V, 5V) to supply power to the internal oscillation circuit. Voltage fluctuations should be controlled within ± 5% range, otherwise it may cause vibration stoppage or frequency drift.

Identification technique: Active crystal oscillators usually have dots, grooves, or silk screen markings at pin 1, and when the pins are facing down, they are in the order of 1-2-3-4 in a counterclockwise direction.

2. Four pin passive crystal oscillator: a resonant component used only as a frequency reference

Passive crystal oscillators are essentially quartz crystal resonators that cannot produce oscillations on their own and rely on external oscillation circuits to drive them. Only two of the four pins are functional:

Pin 1 (Xin): Signal input terminal, connected to the output terminal of an external oscillation circuit, receives a driving signal to excite the crystal to generate mechanical resonance.

2-pin (GND/NC): Grounding or empty pin. Grounding can enhance circuit stability and anti-interference ability. In some models, this pin is empty and only serves as a mechanical fixation.

3-pin (Xout): The signal output terminal feeds back the crystal resonance signal to the external oscillation circuit, forming a closed-loop oscillation loop and ultimately generating a stable clock signal.

4-pin (GND/NC): Grounding or empty pin, similar in function to 2-pin. Some models have already connected to 2-pin internally to achieve grounding shielding or mechanical reinforcement.

Identification technique: Passive crystal oscillators have no polarity, and pins 1 and 3 can be used interchangeably. Pin markings are usually notches or beveled edges, and some models do not have clear markings. The connectivity of the functional pins needs to be measured using a multimeter.

3. Core distinguishing points

Source dependence: Active crystal oscillators require independent power supply, while passive crystal oscillators do not require power supply and are driven by external circuits.

Functional certainty: The pins of the active crystal oscillator have fixed functions, and wiring errors can lead to malfunction; Passive crystal oscillators only have pins 1 and 3 as functional pins, while the remaining pins can be suspended or grounded.

Application scenarios: Active crystal oscillators are suitable for scenarios that require high clock accuracy and stability, such as communication base stations and industrial control equipment; Passive crystal oscillators have low cost and low power consumption, making them suitable for consumer electronic products such as smart watches and Bluetooth earphones.

In practical applications, it is necessary to strictly refer to the product data manual to confirm the pin definition, in order to avoid circuit faults caused by misconnection.