Time Keeping with Quartz Crystals
“The only reason for time is so that everything doesn't happen at once only assume he wasn’t talking about synchronised global networks when he made this comment!
Relationship between Phase Noise and Bit Error Ratio (BER)
As stated in the article ‘relationship between phase noise and jitter' the Phase Noise of a stable crystal oscillator can be converted to an Rms jitter figure. This Rms jitter figure can be analysed further to show the contribution the crystal oscillator makes to the overall system Bit Error Ratio.
Variance as applied to Crystal Oscillators
Before we can discuss variance as applied to crystal oscillators we need to understand what a Variance is, or is trying to achieve. In simple terms variance tries to put a meaningful figure 'to what actually receive’ against ‘what we expect to receive'. It is, simply, a mathematical formula applied to a set of data points / samples / readings which are usually collected over a specified period of time.
Single Transistor Crystal Oscillator Circuits
For an electronic circuit to oscillate there are two criteria which must be satisfied. It must contain an amplifier with sufficient gain to overcome the losses of the feedback network (Quartz Crystal in this case) and the phase shift around the whole circuit is 0o or some integer multiple of 360o. To design a crystal oscillator the above has to be true but there are a myriad of other considerations including crystal power dissipation, unwanted mode suppression, crystal loading (the actual impedance the crystal sees once oscillation has started) and the introduction of a non-linearity in the gain to limit the oscillation build-up.