Quartz Crystals Up To Snuff For IoT Apps

Quartz crystals play a critical role in a plethora of both legacy and current applications. Most common are providing the timing and tuning for real-time clocks and processors, which can be found in nearly every device today. It stands to reason that the Internet of Things (IoT) will also be calling on these humble timing devices for andequally wide range of applications that include wearable components and wireless devices.


Crystals, being small bits of mineral, in this case Quartz, are not always known for being extremely accurate. They are prone to deviations from spec due to heat, cold, pressure, humidity, and shock. However, most current components are achieving impressive levels of precision and reliability, two attributes that are critical, particularly in IoT ventures.


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Addressing the demand for reliable crystals, Abracon, LLC offers the ABM8W, ABM10W, ABM11W, ABM12W, ABS07W, ABS06W family of quartz crystals. The company claims its components specify the industry’s lowest CL and ESR figures. Why are these figures important?


What is CL And What Needs Consideration?


The abbreviation CL refers to the nominal load capacitance of a quartz crystal. Load Capacitance is an important spec depending on the oscillation circuit being used, a common circuit being one that operates in parallel-resonant oscillation mode. Without going too far into design concepts, CL, higher or lower, impacts the desired frequency of the oscillator. Load capacitance is not a bad thing; it just needs to be within the desired tolerances of the designer’s application. In the case of various IoT, IIoT, portable, and wearable designs, lower is better, hence, the company’s offerings claiming the lowest CL.


ESR And How It Affects Performance


Measured with a dedicated crystal impedance meter, equivalent series resistance (ESR) is probably a bigger concern than CL. Whenever resistance comes into the picture, we think a drop in voltage and/or current and heat generation. Engineers sometimes view the crystal as a series circuit containing a capacitor, an inductor, and a resistor, with the resistor representing the resistive element of the crystal. And that resistance is the internal resistance of the crystal, a.ka., ESR.


Like the aforementioned power drop and related heat, high ESRs translate into losses within the crystal. ESR figures are expressed as maximum values in Ohms. The ESR values vary with frequency, mode of operation, housing/packaging, crystal plate size, and electrode size.


A more exact way of looking at is ESR is the impedance of the crystal, and impedance varies with frequency. As a verification of such, ESR values vary with frequency, function, crystal size, electrode size, and housing. The higher the impedance (or ESR), the harder it is for the oscillator circuit to drive the crystal. This can lead to an array of problems including false or slow oscillator starts, inaccurate oscillations, odd operations, etc.


ABMxW and ABSxW Series


Abracon’s comprehensive ABMxW and ABSxW Series crystals lay claim to exhibiting the industry’s lowest CL figures. These are 4 pF for MHz crystals and 3 pF for tuning fork crystals. In terms of ESR, the company guarantees the lowest values on the market. As ESR varies with frequency, the example below shows standard ESR figures for an ABM10.


Frequency (MHz)                   ESR(Ω) max.

12.000 – 15.999                      250

16.000 – 19.999                      150

20.000 – 29.999                      100

30.000 – 55.000                      70


Depending on the model, the components sport a maximum height of 0.4 mm and operating temperature options include -40°C to +125°C. Target applications include industrial, manufacturing, IoT, wearables, and portable wireless.


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