How To Specify

This guide is intended for electronics engineers who may not be fully familiar with specifying quartz crystals and offers general guidance. TechPoint Golledge supplies two main types of crystal, AT cut and tuning fork; for specific advice please contact our Applications Support Team.

Crystal oscillators come in many different types, the most basic is the Clock Oscillator. Here we are not talking about discrete circuits but a single component that is actually a module containing a crystal and a chip that provides the oscillator circuit, including the load capacitors for the crystal and the output buffers.

VCXOs are Clock Oscillators that come with the addition of a tuning function. They allow for fine-tuning of the output frequency by varying the control voltage, making them useful in applications that require precise frequency adjustments

TCXOs are Crystal Oscillators that come with the addition of a tuning function that is designed to cancel out the drift in the output frequency caused by variation in the temperature of the device. Voltage Controlled Temperature Compensated Crystal Oscillators (VCTCXOs) have a tuning voltage input which allows for external tuning in addition to the tuning required for temperature compensation.

OCXOs are Crystal Oscillators situated inside an oven that keeps them at a constant temperature. This relies on the oven temperature being hotter than the maximum ambient temperature. Because temperature variation of the crystal oscillator is almost eliminated, OCXOs can be more accurate than TCXOs. The drawback is the oven requires considerable extra current consumption, particularly while the oven is warming up. The oven also adds bulk to the component.

The first part of selecting an RF filter is selecting what technology to use. The main types stocked by Golledge are SAW and Crystal. We also have a range of ceramic resonator and LTCC LC filters. All our SAW and Crystal filters are bandpass types. There is an overlap between Crystal filters and SAW filters between 35MHz and 110MHz. this being the top of the standard crystal filter range and the bottom of the SAW filter range, 70MHz being popular for both SAW filters and crystal filters. For this centre frequency the choice is made by required bandwidth. SAW’s have bandwidths of 50kHz and higher, while crystal filters have bandwidths up to 30kHz.

Custom SAW filters are very much more expensive to design than Crystal filters. We would therefor ask that customers check that there are no standard parts that can be used before asking for a custom part. Custom SAW designs attract an NRE.

This guide in intended for electronics engineers who may not be fully familiar with specifying SAW resonators and offers general guidance. It assumes at least a basic understanding of RF circuit design; for specific advice, please contact our Application Support Team.

SAW Duplexers consist of a pair of different SAW filters connected together at one end. The node that has the filters connected together is usually connected to an antenna that is used for transmit and receive. This node is usually referred to in specification sheets as the antenna port. Refer to the application note on SAW filters on specifying the individual filters. Custom SAW Duplexers are expensive to design; we would therefore ask that customers check that there are no standard parts that can be used before asking for a custom part. Custom SAW designs attract an NRE.