system: ■ Small form factor – smaller crystals typically have higher ESR, which can impact power consumption ■ Tolerance and stability – the tighter the required stability, the narrower the operating temperature range. Enhancing one aspect will impact the other ■ Power considerations – lower ESR and load capacitance options add significant complexity to the oscillator design. Achieving reliable crystal startup and continuous oscillation will require precise design accuracy ■ Load capacitance – load capacitance (CL) refers to the external capacitance in parallel with the crystal, as determined by the combined capacitances of the circuit, including input, output, and stray capacitances. It plays a critical role in the accuracy and functionality of a quartz crystal. For the circuit to resonate at the correct frequency, the circuit’s capacitance must match the crystal.
grandfather clock, not a wristwatch. Obviously, that would be rather impractical in terms of production and use so there’s a special trick. Watch crystals are designed to resonate at a frequency of 32.768kHz, chosen specifically because it can be easily deduced to one hertz. By passing the 32.768kHz signal through 15 consecutive flip-flops in series, the frequency is halved with each stage, eventually producing a precise one hertz output, or one-second interval. This allows accurate tracking of time, including day, date and seconds. The compact and easy-to-manufactured tuning fork crystal achieves this frequency through a combination of simple arithmetic and the physical dimensions of the quartz blank. Choosing the right tuning fork crystal Although all tuning forks resonate at the same 32.768kHz frequency, selecting the right one isn’t as straightforward as it seems. As mentioned earlier, several factors come into play. In your design, you need to consider board space, required accuracy and power consumption. Each of these involves trade-offs that must be carefully balanced. Below are some areas to consider when evaluating tuning fork crystals for your design
■ Equivalent Series Resistance (ESR) – Equivalent Series Resistance (ESR) is the electrical resistance of a quartz crystal in series resonance, measured in kilo-ohms (KΩ). It’s a crucial factor when selecting a crystal, as it impacts the crystal’s ability to start and maintain oscillation. A higher ESR requires more current for startup, while a lower ESR reduces power consumption during oscillation. ■ Performance and parabolic temperature curve – due to their unique shape, tuning fork crystals are not highly accurate over a wide temperature range. Stability follows a parabolic curve as temperatures deviate from room temperature, with accuracy significantly worsening at extreme highs and lows. A common parabolic coefficient for a 32.768kHz tuning fork crystal is 0.04 ppm/°C². If you need assistance choosing an appropriate tuning fork crystal for your design system, ECS Inc.’s dedicated engineering team can help you find a solution.
Tuning forks for medical applications
Written by David Meaney, Vice President of Global Technical Sales and Marketing at ECS Inc.
resonance, frequency control and application. When an electric current is applied, the crystal vibrates at a precise and stable frequency, typically 32.768kHz . This frequency is ideal because it is power-efficient and can easily be divided down to a one- second signal for timekeeping. The frequency is controlled by the size, shape and mass of the tuning fork’s tangs. Achieving the 32.768kHz frequency in a compact quartz crystal is critical, as a crystal resonating directly at one hertz would need to be so large it would resemble a component for a
What is a tuning fork watch crystal A tuning fork crystal, also known as a watch crystal, is a quartz crystal used to maintain accurate time in clocks, watches and modern electronics like real-time clocks (RTCs) in computers. Its design is inspired by a musical tuning fork, resonating at a precise frequency determined by the mass and dimensions of its two tangs. There are multiple elements that bring together the functionality of a tuning fork crystal such as
Figure 1 shows an example of a parabolic temperature curve.
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