Why do all clocks use 32.768KHz crystal oscillators?
1. Introduction to 32.768KHz Crystal Oscillators
32.768KHz is a standard frequency. The key parameters for crystal oscillator applications include size, load capacitance, frequency deviation, and application range. By form, they are mainly divided into through-hole and surface-mount types: through-hole models include DT26, DT38, 49s, etc.; there are various surface-mount models, with options tailored to different companies’ designs. They are widely used in electricity meters, water meters, gas meters, heat meters, and industrial control instruments.
2. Why Do Clocks Use 32.768KHz Crystal Oscillators?
Why do microcontrollers have multiple external crystal options, while clock crystals are always 32.768KHz? Clock frequency is a critical concept—if a system uses an external crystal, it can obtain other clock frequencies through frequency multiplication or division based on this crystal. In clock systems, the second is an important time unit, and 1 second corresponds exactly to a 1Hz signal. To improve time accuracy, this 1Hz signal must be precise.
In the digital world, there are only two states: 0 and 1. Consider the following calculation: 2¹⁵ = 32768 = 32.768KHz. In reverse, dividing a 32.768KHz clock frequency through 15 binary divisions yields a signal of exactly 1Hz.
3. Characteristics of 32.768KHz Crystal Oscillators
- Frequency Stability: Leveraging the physical properties of quartz crystals, the frequency accuracy is typically within ±20ppm (parts per million), and high-precision models can reach ±5ppm.
- Frequency Division Performance: With a frequency of 32,768Hz (2¹⁵), it can directly generate a 1Hz signal via binary division circuits, making it widely used in timing scenarios such as clocks and electronic devices.
- Package Types: Includes through-hole (e.g., 2×6mm, 3×8mm) and surface-mount (e.g., 49SMD, DST310S) forms to meet different circuit design needs.
- Temperature Range: The typical operating temperature range is -40°C to +85°C, with some high-end models supporting wider temperature ranges.
- Low Power Consumption: The typical power consumption is only 0.5μA~5μA, suitable for battery-powered devices (e.g., smart watches, IoT devices).
- Size Advantage: Miniaturized design, adapting to the space requirements of high-end electronic products.