Last revised: November 4, 2024

Reviewed by: Scott Orlosky, consulting engineer

IC clocks are semiconductor integrated circuits (ICs) that are designed to keep time. IC clocks are important components in virtually all electronic components. They maintain synchronization and timing control in:

• Telecommunications applications
• Consumer electronics
• Wireless handhelds
• Global positioning systems (GPS)

IC clocks may be part of a printed circuit board (PCB) that uses a number of these components. IC clocks can also be used when an input reference clock fails to operate properly. The integrated circuit continues to maintain an accurate clock until the failure of the reference clock is stabilized.

Types of IC Clocks

There are two types of IC clocks: silicon-based timing devices and quartz-crystal oscillators.

• Silicon-based IC clocks accurately align a reference clock signal with a clock distribution signal.
• Quartz crystal-based oscillators are also used as timing devices in electronics equipment.

Both silicon-based IC clocks and quartz-crystal IC clocks are used in many applications. IC clocks that are semiconductor-based include phase-locked loop clock drivers and buffers. A phase-locked loop (PLL) timing device is used in a variety of ways, including for the recovery of clock-timing information from a disk drive, or to maintain timing relationships between processor elements that operate at faster speeds than external signals.

Applications

IC clocks are an important electronic component in mobile and handheld devices such as digital cameras, video cameras, handheld gaming systems, mobile phones, home security systems, and global positioning systems (GPS). Digital IC clocks have chips that are used in high-speed data communication devices such as audio multiplexers too. IC clocks can also be used in automotive or industrial applications.

Specifications

IC clocks destined for sale in Europe must comply with RoHS. Reduction of Hazardous Substances (RoHS) is a European Union (EU) directive that requires all manufacturers of electrical and electronic equipment sold in Europe to demonstrate that their products contain only minimal levels of the following hazardous substances:

• Lead
• Mercury
• Cadmium
• Hexavalent chromium
• Polybrominated biphenyl
• Polybrominated diphenyl ether

Standards

UL 826 — Household electric clocks.

BS EN 60335-2-26 — Household and similar electrical appliances — safety — Part 2-26: particular requirements for clocks.

IC Clocks FAQs

How do different types of IC clocks vary in terms of accuracy and stability?

When considering the accuracy and stability of different types of IC clocks, several factors come into play.

The accuracy and stability of IC clocks can be significantly affected by temperature changes. For example, oscillator circuits can maintain stability by using temperature compensation techniques, such as calibration with a look-up table and correction coefficients.

Real Time Clock (RTC) modules, like the ECS-RTC-3225 series, are designed to minimize the effects of temperature, pressure, and humidity. They offer stability over a wide temperature range, with specific ppm (parts per million) deviations depending on the model and temperature range.

Quartz Crystal Oscillators: These are known for their high accuracy and stability. They achieve 1 ppm accuracy almost immediately upon startup and maintain stability across various conditions. They are less affected by temperature swings, shock, and vibration compared to other technologies.

MEMS Oscillators: Offer advantages in terms of size and integration. MEMS oscillators have steadily improved in performance and have become a standard reliable and stable option for everyday use. They are still not as good as quartz in terms of phase noise and cost, but they are more rugged and can be very small for tight spaces.

The long-term stability of IC clocks can be influenced by aging. For instance, the performance of RTC modules may deteriorate over time due to aging effects, although hermetic sealing and integrated crystal resonators can help mitigate these effects.

Jitter, which is the fluctuation in the timing pulses, is a critical factor in determining the stability of a clock. Quartz oscillators typically offer superior jitter and phase noise performance, making them ideal for applications requiring clean timing signals.

In summary, quartz crystal oscillators generally provide better accuracy and stability compared to MEMS oscillators, especially in terms of startup characteristics, jitter, and phase noise. Temperature compensation and design considerations are crucial for maintaining stability across different operating conditions.

What are some temperature compensation techniques for IC clocks?

Temperature compensation techniques for IC clocks are crucial for maintaining accuracy and stability across varying environmental conditions. Here are some insights:

One method to achieve temperature compensation is through the use of software routines that implement calibration. This involves creating a look-up table with correction coefficients that adjust the clock signal based on temperature variations. This technique requires individual calibration at the PCB level to establish a clock count versus temperature relationship.

While calibration can correct for many temperature-related errors, temperature hysteresis error presents a challenge. This error is similar to the retrace error of a capacitor and is not easily calibrated because its magnitude is typically not repeatable and depends on the temperature history.

For Real Time Clock (RTC) modules, such as the ECS-RTC-3225 series, hermetic sealing and integrated crystal resonators help minimize the effects of temperature, pressure, and humidity. These design features contribute to maintaining stability over a wide temperature range, with specific ppm deviations depending on the model.

What is the impact of aging on the stability of IC clocks?

The impact of aging on the stability of IC clocks is an important consideration in their long-term performance.

The performance of IC clocks, particularly those using crystal oscillators, can deteriorate over time due to aging effects. This is because the characteristics of the crystal and the oscillator circuit can change as they age, affecting the clock's stability and accuracy.

Some IC clocks are designed to minimize the effects of aging by incorporating features such as hermetic sealing and integrated crystal resonators. These design elements help protect the clock from environmental factors that can accelerate aging, such as temperature, pressure, and humidity.

Despite these mitigation techniques, aging remains a factor that can influence the long-term stability of IC clocks. Over time, even well-protected clocks may experience changes in their frequency stability, which can lead to deviations from their specified performance 

What are some of the design features that help mitigate aging effects in IC clocks?

To mitigate the aging effects in IC clocks, certain design features are implemented to enhance their long-term stability and reliability.

Hermetic sealing is a design feature that helps protect the internal components of IC clocks from environmental factors such as moisture, dust, and other contaminants. This sealing helps maintain the integrity of the crystal and oscillator circuit, reducing the impact of aging on performance.

The integration of crystal resonators within the IC clock design helps ensure consistent performance over time. These resonators are less susceptible to environmental changes, which can otherwise accelerate aging effects. By maintaining a stable frequency, they contribute to the long-term stability of the clock.

Implementing temperature compensation techniques, such as using look-up tables with correction coefficients, can help adjust the clock signal to account for temperature variations. This compensation is essential for maintaining accuracy and stability, which can be affected by aging.

These design features are aimed at minimizing the effects of aging and ensuring that IC clocks maintain their specified performance over extended periods. However, it is important to note that while these features can mitigate aging effects, they cannot completely eliminate them.

What are the specific environmental factors that can accelerate the aging of IC clocks?

Temperature

Changes in temperature can significantly affect the performance of IC clocks. The characteristics of the crystal and oscillator circuit can change with temperature, leading to performance deterioration over time.

Pressure

Variations in pressure can also impact the stability and longevity of IC clocks. Hermetic sealing is often used to protect the internal components from pressure changes, which can otherwise accelerate aging.

Humidity

Humidity is another environmental factor that can affect the aging of IC clocks. Moisture can lead to corrosion and other detrimental effects on the clock's components, impacting its long-term stability.

These factors highlight the importance of design features such as hermetic sealing and integrated crystal resonators, which help mitigate the effects of environmental conditions on IC clocks.

What is the role of hermetic sealing in IC clocks?

Hermetic sealing protects IC clocks from various environmental factors.

Hermetic sealing helps shield the internal components of IC clocks from moisture, dust, and other contaminants. This protection is essential for maintaining the integrity of the crystal and oscillator circuit, which are sensitive to environmental changes.

By providing a sealed environment, hermetic sealing minimizes the effects of temperature fluctuations, pressure changes, and humidity on the performance of the IC clock. This is particularly important for maintaining the stability and accuracy of the clock over time.

The use of hermetic sealing contributes to the long-term stability of IC clocks by reducing the impact of aging. It helps ensure that the clock maintains its specified performance despite the potential for environmental factors to accelerate aging.

IC Clocks Media Gallery

References

GlobalSpec—White Paper: Quartz Crystal vs MEMS Oscillators Performance Based on Real Applications

Image credits:

Texas Instruments High-Performance Analog | 1-Source Electronic Components