PARTNERFOCUS
Lack of availability of ceramic packages forces crystal rethink
In these times of Covid supply chain problems many new challenges are having to be met by component engineers. To maintain production, engineers are being forced to consider redesigns to accommodate the differing characteristics inherent in smaller package variants. Here Andy Treble, Sales and Marketing Director at Euroquartz Group, highlights some of the issues that may be encountered
lack of availability of 7x5mm size ceramic crystal packages. An obvious solution is to drop down a package size to 5x3.2mm, but this needs to be approached with care as a stable design may be affected by the introduction of a smaller package.
O
ne of the biggest issues being faced in the market currently for instance is the
The selection of the optimum crystal for
any design is always influenced by several different parameters, not the least of these being the physical dimensions of the crystal itself. A difficulty here is that in general a crystal’s package size and ESR are inherently linked by the fundamental relationship between two specifications: the smaller the package size, the higher the crystal Equivalent Series Resistance (ESR) will be. Oscillator circuits utilising high ESR crystals require careful design to ensure a low drive current and, more importantly, some of the more popular and simple oscillator circuits can often refuse to start oscillation if a crystal with too high an ESR is employed. It should also be noted that it is good practice to test the circuit over the desired operating temperature range to make sure that the circuit operates correctly over the entire span.
48 SEPTEMBER 2021 | ELECTRONICS TODAY
Many chipsets used often employ noise generation within the chipset to drive the crystal, but this may not always be a constant level and is, very often, an unmeasured parameter. This can result in a lack of reliability caused by batch variation failures. This is because there will be an optimum ESR for any circuit and if this optimum happens to fall within the middle of a crystal batch spread then a percentage of the crystals may fail if the circuit has insufficient gain to drive the higher ESR crystals. Due to this problem, Euroquartz has seen
30% batch failures in some cases. If this occurs after a design has been released to production one of the few possible solutions has been for Euroquartz, as manufacturer of the crystal, to perform screening of crystal ESR to select out the higher ESR units. This screening procedure can only normally be
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