Diagram for a Sine Wave Generator
This is a
circuit for generating a sine wave from a single operational
amplifier. The feedback loop of the
op amp in this circuit (741) consists
of a twin-T filter connected between its output and its inverting input.
Positive feedback for oscillation is provided by R2.
The twin-T filter
(see Figure 2) is a passive
notch filter composed of two T-networks, with
maximum attenuation occurring at fn = 1/(2πRC). One
of these T networks has one resistor and two capacitors, while the other
has two resistors and one capacitor.
At the
notch frequency fn of the twin-T filter, the total phase shift
around the loop gain of this op amp circuit is zero, which satisfies
the requirement for oscillation. This is why the circuit generates a
sine wave with a frequency equal to
fn =
1/(2πRC).
Note that
variable resistor R3 in the circuit needs to be adjusted (in
relation to the chosen value for R) until oscillation occurs.
A Twin-T Filter
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