RC oscillators are a type of feedback oscillator; they consist of an amplifying device, a transistor, vacuum tube, or op-amp, with some of its output energy fed back into its input through a network of resistors and capacitors, an RC network, to achieve positive feedback, causing it to generate an oscillating

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4. The RC Oscillator Circuit
RC Oscillators use a
combination of an
amplifier and an RC
feedback network to
produce output
oscillations due to the
phase shift between the
stages.

5. The RC Oscillator Circuit
For an RC oscillator to sustain its oscillations
indefinitely, sufficient feedback of the correct phase,
that is positive (in-phase) Feedback must be provided
along with the voltage gain of the single transistor
amplifier being used to inject adequate loop gain into
the closed-loop circuit in order to maintain oscillations
allowing it to oscillates continuously at the selected
frequency.

6. The RC Oscillator Circuit
However in reality it is difficult to obtain exactly 90o of
phase shift for each RC stage so we must therefore
use more RC stages cascaded together to obtain the
required value at the oscillation frequency. The amount
of actual phase shift in the circuit depends upon the
values of the resistor (R) and the capacitor (C), at the
chosen frequency of oscillations with the phase
angle ( φ ) being

7. The RC Oscillator Circuit

8. The RC Oscillator Circuit
The oscillator itself can be tuned to operate in the
frequency range of 20-100 MHz using digital control
signals and this fits the current sensor implementation.

9. The RC Oscillator Circuit
RC phase shift oscillator is used for generating
signals power a wide frequency ra nge. The
frequency can be varied from few Hz to 200 Hz by
employing one set of resistor with three capacitor
ganged together to vary over a capacitance range in
the 1:10 ratio.

10. The RC Oscillator Circuit
The frequency of oscillation is determined by the
Barkhausen criterion, which says that the circuit will
only oscillate at frequencies for which the phase shift
around the feedback loop is equal to 360° (2π radians)
or a multiple of 360°, and the loop gain (the
amplification around the feedback loop) is equal to
one.