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matched by the gain of a transistor or valve. The output of this filter
is connected to the input of the amplifier, whose output is connected
to the input of the filter, as in Fig. 14.15.
HI—rHI-
T II τ IHî—°
OUT
Fig. 14.14 Three-stage CR filter circuit for
obtaining the 180° phase shift required by
a self-oscillator
Fig. 14.15 The filter in Fig. 14.14 can be
developed into an oscillator by connecting
a simple amplifier between OUT and IN
I
1 1 ΪΤ I
This type of oscillator has a rather limited use, because the
component values and the active device have to be well chosen to
ensure oscillation; varying the frequency of oscillation is not