The size and frequency stability of clocking pruducts influence the dimensions and power consumption of an end device. The developers of battery-operated products in particular require precise and compact frequency generators – an overview of the current state of technology in the oscillating quartz market.
Quartz crystals (or just quartz) was developed into practicable quartz for use in radio engineering at the start of the 1920s. Today, we simply can’t do without quartz in our modern, technological lives. Over recent years, there has been a significant transition from large THT (Through-Hole-Technology) and SMD quartz (Surface Mounted Device) in metal housings for miniaturised SMD quartz in ceramic housings. The need for higher-frequency oscillating quartz in smaller housings has been a big driver for this trend. Thanks to technological advances and several innovations in production, it became possible to significantly reduce the structural size of the oscillating quartz without cutbacks on performance or increased costs.
At the moment, the form factor 3.2 x 2.5 mm is used a lot in all kinds of applications, mainly in connection with resistance optimisation of the quartz for the optimal oscillation behaviour in the defined working temperature ranges and in the frequency range of 8.0 to 64.0 MHz (AT base tone). They can be operated with a drive level of up to 500 µW (in the frequency range from 12.0 to 64.0 MHz). For particularly demanding applications, components with frequency tolerances of up to ±10 ppm and a temperature range of -55 to 125 °C are available.
In past years, the SMD quartz in ceramic housing with the dimensions from 2.5 x 2.0 mm housing (4 pad) to 3.2 x 2.5 mm housing (4 pad) developed in parallel, but never really caught on. If a 3.2 x 2.5 mm housing is too large, you can rely on the high-volume product in 2.0 x 1.6 mm housing (4-pad). This housing type is on trend for very small applications. The quartz design in this form factor is also resistance-optimised and designed for the optimal oscillation behaviour. The developer can use versions with a drive level of up to 400 µW.
The trend towards smaller housings and a greater frequency stability is also evident in the as well. The smallest version with the dimensions 1.2 x 1.0 mm is just about to be released. 32.768 KHz quartz in 3.2 x 1.5 mm housing and 2.0 x 1.2 mm with reduced resistance is seen a great deal now in end devices. Low-resistance quartz with 32.768 kHz and also the standard versions are available on the quartz market with load capacities from 4 to 12.5 pF in the temperature range from -40 to +125 °C. The developer can select between two frequency tolerances at +25 °C: ±10 ppm (optional) or ±20 ppm (standard).
More and more IC manufacturers are basing their work on SMD quartz with integrated thermistors, for example in a 2.0 x 1.6 mm ceramic housing. This quartz is used more and more in battery-operated communications products and replaces power-consuming (up to 2 mA) temperature-compensated quartz oscillators (TCXO).
It may therefore be concluded that in recent years, things that seemed impossible have occurred in the development of quartz. Progress was made in the miniaturisation of housing sizes without a loss in performance or increase in cost and the technological advances of the electronics sector were used to support getting more and more innovative solutions in product design ready for the market. The result is an ever greater frequency stability with housing sizes that are getting smaller and smaller.
