Base Bias Constant Voltage Source

As a result of a reference I saw in a reply to one of my earlier posts, I
bought the book "Radio Frequency Transistors" by Dye and Granberg. At the
bottom of page 61 they say " ... the base bias supply must be able to supply
current without considerable excursion in the base-emitter voltage between
the no signal and the maximum signal conditions. This requires a constant
voltage source, as variations of a few millivolts represent a large portion
of the nominal 0.63-0.67 volt typical value."

My question is; how can a variation of a few millivolts have an appreciable
impact on the base-emitter voltage when the bias can be set at 2,3,4 or more
volts to begin with? I t would seem to be negligible in terms of the amount
of main bias voltage present on the base.

Second question: Exactly how can the low voltage signal (say 100 milivolts
peak) affecting the bias in any significant way to begin with?

Third question: What impact is all this having on a common emitter circuit
set up for linear amplification?

Any help in understanding this will be much appreciated.


.

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