Quartz oscillators - what are they and how do they work?

Although we may not realize it, most electronic devices would not function without being able to measure time accurately. What gives them this ability are small and inexpensive, but extremely important quartz resonators. In this article, we will introduce you to a group of components that make almost all of today's clocks, microprocessors, and a wide range of other devices work.

Why was the invention of the quartz oscillator revolutionary?

With the invention of radio communication at the end of the 19th century, there was a need to precisely control the frequency of transmitters and receivers. This was necessary in order to transmit and receive information efficiently, without interfering with other devices. The original wireless radios and telegraphs used LC resonators for this purpose - resonant circuits consisting of an inductor and a capacitor. However, these resonators were prone to detuning - they could easily drift off their frequency, mainly due to temperature changes. This caused serious problems, including interference between adjacent radio channels and the need for frequent tuning of the receiver [caption id="attachment_74287" align="aligncenter" width="1200"] LC resonator schematic. Its frequency depends on the capacitance of the capacitor and the inductance of the coil.[/caption] Resonators based on quartz crystals were developed as early as the 1920s. Due to their much higher frequency stability, they quickly became the standard in radio engineering of that time. They also used to be the most accurate devices for timekeeping, until the invention of the atomic clock. Initially, quartz resonators were made from crystals of natural origin. The increasing demand for this resource, especially during World War II, initiated research into the production of synthetic quartz. The development of the hydrothermal method in the 1950s made it possible to grow synthetic quartz crystals in mass quantities. Today, virtually all crystals used in electronics are produced synthetically.

How does a quartz oscillator work?

A quartz resonator takes advantage of the piezoelectric properties of a quartz crystal. The piezoelectric effect consists in the appearance of an electric charge on the surface of the crystal due to mechanical stress, and, conversely, its deformation when an electrical field is applied to it. Crystals used in oscillators have a pair of thin electrodes attached to them. Thanks to them, the vibrations of the crystal can be easily transformed into an electrical signal and vice versa. The quartz resonator, together with a circuit that excites and sustains its oscillations, is called a quartz oscillator. At the oscillator startup, the crystal is set in vibration by electrical signal - this can be compared to the striking of a tuning fork. Due to its natural resonance frequency, the crystal acts like a band-pass filter - it keeps the oscillations close to this frequency, attenuating all others. The resonance frequency is defined by several factors - including the shape of the crystal (e.g. bar, disk or tuning fork), its size and the way in which the oscillations propagate within it. [caption id="attachment_74290" align="aligncenter" width="1200"] Removing enclosure from the crystal resonator reveals a disk-shaped quartz crystal with electrodes connected to it[/caption] The signal from the electrodes of the oscillating crystal is amplified by the oscillator circuit and then fed back to the crystal - positive feedback occurs. With each cycle the oscillation becomes stronger and stronger, until they reach their peak value and the system stabilizes. The output of the oscillator is then a stable, usually rectangular waveform signal, which can be used, for example, as a timing signal.

Where are quartz resonators used?

Low frequency crystals are most commonly used in real-time clocks (RTC). They can be found in almost all modern electronic and digital clocks, including wristwatches. The most common frequency standard for clock oscillators is 32.768kHz. Crystals used in clocks usually come in cylindrical, through-hole mounted packages, but there are also much smaller, surface-mounted variants. Crystals with frequencies ranging from a few to tens of MHz are the most popular ones. They are widely used in digital electronics to generate timing signals for microcontrollers, interfaces, and wireless communication systems. Quartz oscillators can be found in almost all devices that need accurate time or frequency measurement. [caption id="attachment_74292" align="aligncenter" width="1200"] The 12MHz crystal (Q3) visible on the picture is responsible for clocking the STM32 microcontroller. Additional crystal (Q2) is a part of the real-time clock circuit.[/caption] Another group are Surface Acoustic Wave (SAW) resonators, with frequency range from tens of MHz up to several GHz. They are mainly used in radio communication, for frequency stabilization and as high-efficiency filters. Similarly as in the case of other quartz resonators, they are characterized by high accuracy and frequency stability at a relatively low cost. A single SAW resonator allows precise selection of the operating frequency of the transmitter or receiver, but does not allow for any frequency adjustment. This makes them ideal for inexpensive remote control devices, such as garage door openers, and remotes for various home appliances. They are also used in radio devices operating in ISM bands, as well as TV receivers. Let's take a look at an example of a SAW resonator - our WTL2Y36723PZ 433.92 MHz resonator. It's an effective solution dedicated for remote controls - it allows you to design a simple and inexpensive radio transmitter or receiver using a small number of components. In the table below, we present the most important parameters of the WTL2Y36723PZ resonator:

Symbol	WTL2Y36723PZ
Type	SAW resonator
Frequency	433.92MHz ±75kHz
Mounting method	SMD
Package	3.2×2.5mm
Operating temperature range	-40°C÷+85°C

We invite you to browse our offer of quartz resonators and ceramic filters from InterElcom. In case of any questions, feel free to use our contact form.