Direction for [ Question No: 1 To 5 ] :
Read the following paragraph and answer the questions :
An oscillator having initially been set at a particular frequency will generally drift and wander about in frequency. The frequency stability of an oscillator is a measure of its ability to maintain as nearly a fixed frequency as possible over as long a time as possible. These deviations of frequency arise because the values of critical features, on which the oscillator frequency depends, do not remain constant in time. The critical features include circuit components, transistor parameters, supply voltage, stray capacitances etc. Accordingly, an obvious but clearly useless solution of the problem of making a frequency stable oscillator is to keep all these features constant. In the first place, the number of circuit features is very large and some of the features like transistor parameters are inherently unstable and extremely difficult to keep constant. Moreover, it is hard to know where stray circuit elements and couplings are located and how to estimate their magnitudes. Thus making it difficult to maintain them constant.
However, it is recognized that in every oscillator circuit there are relatively few circuit features on which the frequency is sensitively dependent, whereas the frequency dependence on the far larger number of features is comparatively slight. For example the frequency of phase shift oscillator primarily depends on R and C and other parameters do not affect it too much. In a parallel resonant circuit the impedance changes from an inductive to a capacitive reactance as the frequency is increased through resonance point. If the Q is infinite this change in phase is abrupt. Hence a tuned circuit oscillator will have excellent frequency stability independent of temperature, current etc.
