[time-nuts] Looking for datasheet for Oscilloquartz 8602

Tom Van Baak tvb at LeapSecond.com
Sat Jun 1 13:11:58 EDT 2013


>> Far more significant than any of that - marketing may well have asked that
>> the part be optimized in a different way so it would sell better. Phase
>> noise often seen as a better "bragging rights" spec than ADEV. My personal
>> opinion is that this bias is driven more by the fact that fewer people
>> understand (or trust) ADEV and it's derivatives. 
> 
> Could you explain a little bit more about ADEV vs phase noise?
> 
> Attila Kinali

Someone else can provide a long answer, but here's a short one.

ADEV is a good statistic to use if your goal is any sort of timekeeping, where performance over seconds or hours or days is important. But many applications, especially modern ones, need oscillators not so much for timekeeping but for frequency transmitting, receiving, multiplication, or sampling, where performance over nanoseconds to milliseconds and purity of waveform is important. In this case jitter and phase noise are a better measurement to use than ADEV.

The other key point is that ADEV is an accumulated error over time (by integration time, tau) statistic while phase noise is spectral density (by frequency bin, Hz) statistic. Either way, it's important to understand that you can make any measurement you want on a given oscillator; but the one that really matters is the one required for the device to operate within its spec. If buying an oscillator for an ADC or DAC clock, you are more interested in jitter and phase noise than gradual accumulated time or frequency drift. If buying a timebase for a chronometer, or building a master clock for a national timekeeping laboratory, you are more interested in long-term ADEV than high-frequency phase noise, etc.

/tvb



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