To non-engineers in our midst, all clocks seem about the same. They know that some are more precise than others, and except for diver’s watches, they don’t work well wet. Yet, even for engineers, when it comes to choosing timing devices, there are many variations, and unless you specify the right one, you may wish you’d spent more time on this process.
Given that the timing device selections you make will vary based on your intended application, let’s explore the major considerations and how to ensure you make the best possible decisions.
IoT & Consumer
For many IoT applications, designers choose Crystal Units that are miniature in size and require little power to drive (see Drive Level below). Similarly, for consumer applications, such as fitness trackers, there are Real-Time Clocks that are very small and consume little power. But that’s just the beginning.
Frequency — it’s the most important factor in every timing decision. Look at the chipset in your design. That will suggest what range of frequencies you’re allowed to use. Check if there are industry-standard frequencies for your application.
ESR — Equivalent Series Resistance is a reference for the ease of oscillation. Stay within the specification of the chip manufacturer or risk problems such as the oscillation starting too slowly or not starting up at all. For an ESR specification, a lower value such as 60 ohms is often the right way to go. Check in with us if you have more questions about these specifications.
Drive Level — describes the power or oscillation output level required to drive a crystal unit. Driving too much power to the crystal can cause irreversible damage such as cracking the crystal. If the chipset specifies a maximum output level, either match that recommendation or impose a higher maximum drive level for your Crystal specification.
Load Capacitance — the capacitance that fine tunes the frequency of the crystal. If you have the wrong load capacitance, you’re going to shift the frequency. Solution: match the load capacitance of the board to the crystal specification.
There’s a wide range of temperatures that apply to timing devices used in industrial settings. Many applications call for highly reliable and flexible Programmable Oscillators. Keep in mind: If you need your equipment to operate effectively at high temperatures you should choose a crystal or oscillator rated for it, knowing that other timing specifications will also change, particularly the stability specification.
Stability — Whether it’s 100ppm or 20ppm, if there’s a predetermined standard for your application, you just need to match it. Frequency error isn’t additive like noise, so there is no need to select a higher stability part than required. Don’t ignore the temperature specifications – exceeding these temperatures may result in frequency deviations beyond your stability spec. It’s important to remember that the temperature seen by your timing device may be higher than the system ambient temperature. It’s always smart to place crystals away from excessively hot components. Another good idea is to confer with us first.
Monitoring — If your system requires power or event monitoring, you might be able to accomplish that with a small size Real-Time Clock. They’re rated for high temperature and have various monitoring functions, such as event detection and time stamping. RTCs can also aid power management through voltage monitoring and power switching between primary and backup power sources to ensure your MCU is protected. Real-Time Clocks can operate these functions while the processor is asleep, which saves power and extends battery life.
The automotive industry (like other fields) is undergoing a digital transformation on a path toward autonomous vehicles. While not all automotive applications are AVs, we believe those may utilize Temperature Compensated Oscillators that require high stability and reliability.
Reliability — to ensure the part is robust enough for automotive applications, choose a timing part that’s AEC-Q (Automotive Electronics Council) certified or compliant. AEC-Q for timing devices includes two main types: AEC-Q200 for passive products, products that don’t require power such as Crystals. AEC-Q100 for active products, such as Oscillators and Real-Time Clocks, which require power inputs.
Aging — automotive equipment is intended to last 10 years or more. Aging is typically only specified for the first year in the standard specification, where most of the aging happens and it decreases over time. There are +10-year aging performance data available to help you design for your product life expectancy.
5G network equipment is being deployed globally and much of the gear includes Oscillators that deliver low phase noise and jitter, high frequency, high reliability, and very high stability.
Stability — network timing synchronization may require high-stability timing devices like Temperature Compensated Crystal Oscillators (TCXOs). Epson offers TCXOs with as low as 100 ppb over a standard operating temperature. Some networking applications also require unusual or uncommon stability metrics and for those we encourage you to work directly with an Epson expert.
Jitter — in networking applications you need to move data quickly. The faster the data rate, the more important jitter becomes to that design. A lower jitter number is preferable. If you’re working on a system faster than 10Gbps, pay close attention to the phase jitter specification. For a system moving data at 10Gbps, your phase jitter requirement is likely around 300 fs (femtoseconds). For 400Gbps, your system may require as low as 70 fs phase jitter.
Have an important design review coming up? Let’s discuss your requirements. Contact us at your convenience to source the best timing solution for your application.