Design Of Op Amp Sine Wave Oscillators

 Criteria for oscillation
The canonical form of a feedback system1 is shown in
Figure 1, and Equation 1 describes the performance of
any feedback system (an Amplifier with passive feedback
components constitutes a feedback system).  
Oscillation results from an unstable state; i.e., the feed-
back system can’t find a stable state because its transfer
function can’t be satisfied. Equation 1 becomes unstable
when (1+Aβ) = 0 because A/0 is an undefined state. Thus,
the key to designing an Oscillator is to insure that Aβ = –1
(called the Barkhausen criterion), or using complex math
the equivalent expression is Aβ = 1∠–180°. The –180°
phase shift criterion applies to negative feedback systems,
and 0° phase shift applies to positive feedback systems. 
TLV2471 Wien-bridge circuit schematic 

 Bubba Oscillator
 The Bubba Oscillator (Figure 9) is
another phase-shift Oscillator but it
takes advantage of the quad op amp
package to yield some unique advantages.
Four RC sections require 45° phase shift
per section, so this Oscillator has an
excellent dφ/dt to minimize frequency
drift. The RC sections each contribute
45° phase shift, so taking outputs from
alternate sections yields low-impedance
quadrature outputs. When an output is
taken from each op amp the circuit
delivers four 45° phase-shifted sine
waves. The loop equation is:
  TLV2474 Bubba Oscillator
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TLV2471 Wien-bridge circuit schematic
TLV2471  Wien-bridge circuit schematic

TLV2474 Bubba oscillator
TLV2474  Bubba oscillator


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