This circuit will divide the output frequency by some integer - N - to produce a much lower reference frequency. To generate these lower frequencies, a divide-by-N digital counter is provided. The crystal oscillator is usually operated at a frequency such as 5 MHz, but lower frequencies are often needed. The OCXO is capable of 0.1 ppm/year for aging and 0.01 ppm/year for temperature. The TCXO will typically exhibit crystal aging of better then ☒ ppm/year, and a temperature aging of ☑ ppm/year. For that purpose, either Temperature Compensated Crystal Oscillators (TCXO) or Oven Controlled Crystal Oscillators (OCXO) are used for the reference section. The stability of ordinary crystal oscillators is reasonably good for many purposes, but not for use in the reference section of a signal source. The frequency of the reference section must be precisely adjustable over a small range so that it can be compared to a higher order standard, such as a Cesium-beam oscillator or WWVB comparator receiver, for purposes of calibration.īecause it controls the frequency synthesizer, the stability of the reference section determines the overall stability of the signal generator. It is an accurate, stable, fixed-frequency source such as a crystal oscillator. The Reference Section is at the very core of the signal generation process. In Figure 1, each section is broken down into further components for sake of easy analysis. There are three main sections to this signal source: Reference Section, Frequency Synthesizer, and Output Section. This type of signal generator is more modern than the old-fashioned type, and is capable of producing very accurate, high-quality signals. ![]() ![]() ![]() A synthesizer architecture is shown in Figure 1. This time, we will look at the frequency synthesizer. Part 1 of this two-part article introduced the topic of signal generators. » Skip to the Extras Frequency Synthesizers
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