Crystals & Oscillators

Our wide range of oscillators includes Standard, MEMS, SAW, and many other types

The difference between a crystal and an oscillator

In simplified terms, a crystal (sometimes called a resonator) is a moving/resonating passive component that connects to an external oscillator circuit in the chip that it is timing, like an SoC, microcontroller or processor.

By contrast an oscillator is an integrated timing solution that contains both a resonator and an oscillator IC, in one active device.

The eight most important oscillator parameters

The oscillator clock provides the heartbeat on which all other signals in the system are based, so it is important to understand and consider the factors and specifications that most affect these components’ performance. Accordingly, SiTime (whose products are available through our website) has defined eight top parameters:

1. Frequency can be factory programmed by SiTime, programmed by key distributors, or programmed for lower volumes in the customer’s lab using an oscillator programmer.
2. Frequency stability is typically expressed in parts per million (ppm) or parts per billion (ppb) which is referenced to the nominal output frequency. It represents the deviation of output frequency due to external conditions; therefore, a smaller stability number means better performance.
3. Output signal format: Single-ended or differential. Differential signalling is more expensive, but it enables better performance and is preferred for higher frequency applications.
4. Supply voltage, specified in volts (V), is the input power required to operate the oscillator.
5. Supply current is the maximum operating current of an oscillator. It is measured in microamps (µA) or milliamps (mA) at the maximum and sometimes nominal supply voltage.
6. Operating temperature: Products complying with various commercial, industrial, automotive and military temperature ranges are available.
7. Package: Oscillators are usually housed in metal, ceramic, or plastic packages, and are available in a variety of industry-standard package dimensions
8. Jitter is the short-term deviation from an ideal clock signal and is measured in picoseconds (ps) or nanoseconds (ns). Because jitter can be one of the main contributors to system timing errors, it’s critical to account for oscillator jitter when evaluating the total timing budget.

Specifying quartz crystals

Parameters for choosing crystals are similar to, but not identical with those for complete oscillator components. IQD (whose frequency products are available through Farnell) has identified that these parameters include frequency, frequency tolerance, frequency stability, package, operating temperature range, and load capacitance. ESR, ageing, and drive level (power dissipated by the crystal) are also important.