Agilent Crystal Oscillator Testing - White Paper 5991-1734EN c20140717 [5] free download

File name Crystal Oscillator Testing - White Paper 5991-1734EN c20140717 [5].pdf

Keysight Technologies Crystal Oscillator Testing White Paper Introduction A policy concerning the testing of the reference oscillators contained within many instruments such as counters, synthesizers and spectrum analyzers has been defined and adopted in Keysight Technologies service centers worldwide. Quartz crystal oscillators are used extensively in measurement instruments to provide an accurate refer- ence frequency or time base against which measured signals may be compared. There are two characteristics of such devices which users may wish to know: 1. The absolute oscillator frequency once it has warmed up 2. The stability of the oscillator frequency over time. Our standard policy is to test the first parameter (and to adjust where necessary) but not the second. This article is designed to help explain the rationale for this decision. High-stability ovenized oscillators have their stability specified in terms of a drift rate per day. This means that within a 24-hour period the frequency will not change by more than the permitted tolerance over that period. This is in contrast to lower stability oscillators whose aging rate is stated over a month or a year. The frequency may well change in the short term more than the specified amount, but the long-term trend will comply with the specification -- see Figure 1. 2 1.8 1.6 Upper aging rate limit 1.4 Parts per million Relative offset 1.2 1 Trend 0.8 0.6 0.4 0.2 Lower aging rate limit 0 1 4 7 10 13 16 19 22 25 28 Days Figure 1. A representation of the frequency stability of an uncompensated or temperature compensated quartz crystal oscillator. Note how the aging rate would far exceed, or be far less than, specification if measurements were taken over a shorter period than the specified one month for this oscillator. The apparent aging rate would also vary considerably depending when the measurements were made. Experience Our company manufactured precision crystal oscillators for many years and d