Popular science essentials | Why is a 32.768kHz crystal oscillator used in quartz watches?

2024-10-18

问题

Why do quartz watches use 32.768kHz crystal oscillators?

built-in2x6 32.768kHz

Quartz watches use a 32.768 kHz crystal oscillator because this frequency strikes the best balance between accuracy, power consumption, and circuit design.

The specific reasons are as follows:

The convenience of binary counting

32.768 kHz is 215 Hz, which means it is exactly 2 ^ 15. This frequency can be conveniently reduced to 1 Hz (i.e., one pulse per second) by a simple crossover circuit, which exactly corresponds to the second hand in the watch.

The specific process is to divide the frequency of 32.768 kHz by one-half of 15 times through a frequency divider:

This binary crossover is simple and efficient, making it particularly suitable for small devices such as watches.

Low power consumption

Quartz watches are battery-powered, and using a crystal oscillator at 32.768 kHz not only provides sufficient accuracy, but also keeps power consumption low. The higher the frequency, the greater the power consumption; and the lower the frequency, the more complicated the circuit design becomes. So 32.768 kHz is a good compromise.

High precision and stability

The 32.768 kHz frequency is an easy to fabricate and relatively stable frequency for quartz crystals. Quartz crystals oscillate very stably at this frequency and can maintain high time accuracy. Although there are factors such as temperature and aging, overall, the crystal oscillator at this frequency has good stability.

Tradition and standardization

32.768 kHz has become the standard frequency in watches and other low-power devices. Using this frequency of crystal oscillators makes it easier for manufacturers to design and manufacture related electronic components, and also reduces production costs and design complexity.

Overall, the 32.768 kHz frequency strikes a good balance between accuracy, power consumption, design simplicity, and component size, making it the most commonly used crystal frequency for quartz watches.

A manifestation of precision

The annual error of an ordinary quartz watch is usually between ± 10 and 20 seconds, which translates to a daily error of about 0.5 seconds. If the frequency of the crystal oscillator is slightly deviated, this error may become even larger.

High-end quartz watches use a temperature-compensated crystal oscillator (TCXO) to reduce the effect of temperature on frequency, allowing the watch to maintain high accuracy over a wider temperature range, with annual errors that can be as low as a few seconds.

With the development of technology, the 32.768kHz package size has also evolved from large size to small size. Hangjing not only retains large-size product lines, such as 8038 and 7015 packages, but also provides a large number of small-size 3215, 2012, 1610 package products, which can provide ± 5ppm/± 10ppm/± 20ppm accuracy, support a variety of load capacitance 12.5pF/9pF/7pF/6pF, and provide solutions to different customer needs.