The advantages of crystal resonators, and some of the options available.

    In microprocessor-based systems, there are several different frequency signals used to execute instructions, move data in and out of memory, and interface with external communications.

    A simple embedded controller might have a clock frequency of a few MHz, while a microprocessor in a personal computer typically expects an input frequency of 15MHz. This will be doubled internally to provide the frequency of the CPU and other subsystems. Other components in the system may have their own frequency requirements. For example, an Ethernet network controller requires a frequency of 25MHz, or a real-time frequency (RTC) of 32.768kHz

    Radio frequency (RF) systems require an accurate frequency reference to enable end-to-end communication and filter unwanted signals and noise.

    Key Oscillator Features

    In addition to the basic requirement to provide a specified frequency, depending on your product's application, the oscillator may need to meet other requirements.

    For example, many products use very precisely defined frequencies. This is especially important for systems that need to communicate with other devices via serial or wireless interfaces. Accuracy is usually measured in parts per million (ppm).

    Low power consumption is very important for handheld or battery powered devices. This is especially true for RTCs as this part of the circuit will always be in a useful state even in low power or standby mode.

    After all, you may need to consider various factors such as operating environment, cost and form factor.

    perfect resonance

    Any oscillator uses some kind of resonant or trim circuit, and adjusts the amplification and feedback to produce a specific frequency output.

    The adjustment circuit can be based on a resistor-capacitor (RC) or inductor-capacitor (LC) network. These devices are relatively simple and the frequency can be varied over a wide range. However, planning an accurate RC or LC oscillator requires the use of valuable and precise components. Even so, they do not meet the highest precision and stability required by many products.

    Crystals (usually in tandem) can also be used as resonant elements. The crystal is cut into two parallel crystal planes and metal contacts are deposited on them. The time-dependent piezoelectric effect means that when a crystal is subjected to pressure, a voltage is generated on its crystal faces. Conversely, when a voltage is applied to the crystal, the crystal also changes shape.

    This feedback will cause the crystal to oscillate at its natural resonant frequency. This will depend on the size of the crystal and how it is cut. The most common cutting method is called AT. This can be used for a wide range of frequency planning and has excellent thermal stability.

    Crystal resonators have a high quality factor (Q ), which means that the frequency is precisely defined and very stable. Therefore, the crystal can serve as the basis for a low-cost, high-precision, oscillator.