I. Basic Definitions
Passive crystal oscillator
Structure: Contains only quartz crystals, with no built-in oscillator circuit.
Working principle: It relies on an external circuit (e.g., the MCU's oscillator) for driving, generating resonant frequency through mechanical vibration.
Active crystal oscillator
Structure: integrated quartz crystal, oscillating circuit and output driver, which can output square wave or sine wave directly.
Working principle: The built-in oscillator operates autonomously with power supply only.
II. Core Differences and Comparisons
|
contrast item |
passive crystal oscillator |
active crystal oscillator |
|
circuit requirement |
requiresanexternaloscillator circuit(e.g.,MCU's OSC_IN/OSC_OUT) |
Worksindependently without external circuits |
|
output signal |
Sinewave(requires shaping circuit) |
Square wave/peak-shaving sine wave (direct drive logic device) |
|
power dissipation |
low (dependent on external drive current) |
High (built-incircuit power consumption, typically 1mA to 50mA) |
|
frequency stability |
±10ppm~±50ppm(affectedbyexternal circuits) |
±0.1ppmto±50ppm(high-precision models can achieve ±0.001ppm) |
|
prime cost |
Low (0.1 to 1 yuan) |
High (1 yuan to 500 yuan, depending on precision and packaging) |
|
start time |
Longer(ms-level, requires an initial vibration process) |
Short (μs level, stabilized upon power-up) |
|
capacity of resisting disturbance |
Weak (dependent on PCB layout and external circuits) |
Strong(built-infilterandvoltage regulator) |
III. Application Scenarios
1. Typical Applications of Passive Crystal Oscillator
Low-cost consumer electronics: such as Bluetooth earphones and remote controls (with MCU clock frequency ≤100MHz).
Embedded systems: The clock source for MCUs like STM32 and ESP32 (requires load capacitor configuration).
Load capacitance formula:
C_load = (C1 × C2) / (C1 + C2) + C_stray (where C_stray represents the parasitic capacitance of the PCB, typically ranging from 3pF to 5pF)
2. Typical Applications of Active Crystal Oscillator
High-frequency and high-precision scenarios:
Communication equipment (5G base stations, optical modules, frequency ≥100MHz).
Precision instruments (atomic clock synchronization, TCXO/OCXO temperature-compensated crystal oscillator).
Complex environment: industrial control (vibration-resistant, wide temperature range-40℃~+125℃).
Direct drive: FPGA global clock and high-speed SerDes interface (e.g., 25Gbps Ethernet).
IV. Key Points in Model Selection
1. Selection of Passive Crystal Oscillator
|
parameter |
Selection rules |
instance |
|
frequency |
Match MCU/Chip Requirements |
25MHz passive crystal oscillator with 20pF load capacitor |
|
load capacitor （CL） |
Match external capacitors according to the chip datasheet specifications |
CL=20pF → C1=C2=2×(20pF - 5pF)=30pF |
|
ESR(Equivalent Series Resistance) |
Low ESR (≤80Ω) reduces the time to start-up |
Select the YSX321SL model with an ESR of 50Ω |
|
package |
Based on PCB space selection (e.g., SMD3225, HC-49S) |
2.0×1.6mm for mobile phone, 3.3×2.5mm for industrial control |
2. Selection of Active Crystal Oscillator
|
parameter |
Selection rules |
instance |
|
Output type |
CMOS(3.3V)LVDS (differential), HCSL (high speed) |
100MHz LVDS output (e.g. YSO230LR) |
|
frequency stability |
Selectbasedon system requirements (e.g., ±10ppm industrial-grade) |
OCXOtemperature-stablecrystaloscillator(e.g. YOV1409SM-10M) |
|
supply voltage |
Matchsystempowersupply (1.8V/2.5V/3.3V/5V) |
YSO110TR with 3.3V Power Supply |
|
phase noise |
High-frequencyscenariosrequire lowphasenoise(e.g., <-150dBc/Hz@1MHz) |
The AI computing power cluster selects YSO212PU |
