Navigating the frequency maze

ESUK Aug13 p30_31_32 AEL 2The complexity of frequency control devices and the vast range of parts available can be daunting for purchasers. To help, AEL Crystals offers a break-down of its portfolio and associated support services

Throughout the specification process, AEL Crystals aims to assist all buyers to ensure that the correct parts are selected. As a start point, the wide range of AEL products can be broken down into various groups, the most common of which are: crystals, oscillators and filters.

Simple timing

Crystal resonators are the simplest form of timing device. AEL offers a host of package and specification options to cover all requirements from simple microprocessor timing solutions through to devices for high stability wireless and radio communications applications. Package sizes include all industry standard surface mount devices (SMD) and through hole parts, with SMD parts available as small as 1.6 by 1.2mm.

In order to supply a product that will work reliably in your application, AEL needs to identify the correct frequency, stability, temperature range, capacitive loading and package size. In many cases this information will be available from the customer’s own database, but if not, AEL is happy to discuss this with customers’ engineers and technical purchasing team to find the most suitable solution.

AEL Crystals also works closely with silicon vendors to specify parts that are suitable for use in a range of applications. Recent developments cover crystals for use in Zigbee applications for Ember and NXP chip-sets and crystals for use in remote keyless entry applications alongside Infineon chipsets.

Understanding oscillators

Oscillators are essentially a crystal element and its driving circuitry combined into a single package. Included within this area are simple clock oscillators as well as temperature compensated oscillators (TCXO), voltage controlled oscillators (VCXO) and voltage controlled temperature compensated oscillators (VCTCXO). A range of output types are available, including complementary metal oxide semiconductor (CMOS), low voltage differential signalling (LVDS), low-voltage positive emitter-coupled logic (LVPECL), high speed current steering logic (HCSL) and Sine wave.

Again these parts are used across a range of applications with clock oscillators used in many commercial and consumer applications. More complex TCXO, VCTCXO and VCXO parts are  used in telecoms, wireless and RF applications demanding more functionality.

To correctly supply these products, AEL must identify the correct frequency, stability, temperature range, input voltage, required output type and package size. For VCXO and VCTCXO parts, the pulling range and control voltage are also required. In many cases there will be additional requirements, such as phase noise, that must also be reviewed.

Experience in supplying parts for RF applications means AEL can offer parts with exceptional stability down to parts per billion levels for emerging telecommunications applications.

Make the most of MEMs

Within this product group, AEL can also supply micro-electro-mechanical systems (MEMs), which are provide a new silicon based oscillator solution. Most current quartz clock oscillator applications can be replaced seamlessly with MEMs oscillators, with no changes to the PCB or effect on circuit operation.

Put simply, MEMs are to quartz what integrated circuits (ICs) are to transistors, bringing frequency control into the 21st century. As a drop in replacement for standard quartz oscillators they differ in using a silicon resonator controlled by an on board ASIC, rather than a quartz blank to derive the output frequency.

MEMs offer a comprehensive product range with a variety of specifications, outputs and package sizes. Outputs include: high speed CMOS (HCMOS), LVDS, LVPECL and HCSL. Various industry standard packages are supplied with temperature ranges: -20 to 70°C to -55 to 125°C.

Furthermore, MEMs oscillators offer a number of advantages over quartz devices and can counter the main weaknesses in quartz technology. Size is a real advantage, since the resonator in a MEMs device measures only 50 by 20µm. Due to the semiconductor construction, MEMs oscillators are inherently more resistant to shock and vibration than qaurtz. Parts also offer improved mean time between failure (MTBF) and failure in time (FIT) performance.

Cost advantages are in evidence, particularly in the differential output devices, where costs can be up to 50 per cent lower than quartz and there are also lead-time advantages. MEMs oscillators are available on short lead-times of typically 24 hours for low quantities and samples and two to three weeks for production volumes. This is applicable to all output types, including differentials, and all package sizes.

Filter the results

Filters are used within most RF and communications equipment. AEL offers a range of standard ceramic and quartz parts, ranging from simple 455kHz ceramic filters through to custom designed devices.

AEL can also offer surface acoustic wave (SAW) devices, antenna for global positioning systems (GPS), global navigation satellite system (GLONASS), Wi-Fi, Bluetooth, satellite digital audio radio service (SDARS) and radio frequency identification (RFID), plus dielectric filters for GPS and RFID and VCO.

When selecting the most appropriate components purchasing should also consider the vendor’s ability to support a customer’s production model, including the design authority and local or offshore production facilities. To this end, AEL Crystals boasts an extensive logistics operation, allowing products to be shipped to customer’s manufacturing sites globally and also supporting local stocking facilities to aid lead-time reduction.