233:
721:
674:
power supply rails. The net effect is the oscillator amplitude will stabilize when average gain over a cycle is one. If the average loop gain is greater than one, the output amplitude increases until the nonlinearity reduces the average gain to one; if the average loop gain is less than one, then the output amplitude decreases until the average gain is one. The nonlinearity that reduces the gain may also be more subtle than running into a power supply rail.
473:
1134:
22:
681:
in the output signal. If the small-signal gain is just a little bit more than one, then only a small amount of gain compression is needed, so there won't be much harmonic distortion. If the small-signal gain is much more than one, then significant distortion will be present. However the oscillator
665:
components is unstable with respect to amplitude. As long as the loop gain is exactly one, the amplitude of the sine wave would be constant, but the slightest increase in gain, due to a drift in the value of components will cause the amplitude to increase exponentially without limit. Similarly, the
225:
together mechanically on the same shaft. The oscillation frequency is proportional to the inverse of the capacitance or resistance, whereas in an LC oscillator the frequency is proportional to inverse square root of the capacitance or inductance. So a much wider frequency range can be covered by a
716:
works in a similar fashion). The lamp both measures the output amplitude and controls the oscillator gain at the same time. The oscillator's signal level heats the filament. If the level is too high, then the filament temperature gradually increases, the resistance increases, and the loop gain falls
176:
needed for the LC oscillator become cumbersome, and RC oscillators are used instead. Their lack of bulky inductors also makes them easier to integrate into microelectronic devices. Since the oscillator's frequency is determined by the value of resistors and capacitors, which vary with temperature,
673:
As the peaks of the sine wave approach the supply rails, the saturation of the amplifier device flattens (clips) the peaks, reducing the gain. For example, the oscillator might have a loop gain of 3 for small signals, but that loop gain instaneously drops to zero when the output reaches one of the
220:
This makes tuning the circuit to different frequencies more difficult than in other types such as the LC oscillator, in which the frequency is determined by a single LC circuit so only one element must be varied. Although the frequency can be varied over a small range by adjusting a single circuit
669:
In most ordinary oscillators, the nonlinearity is simply the saturation (clipping) of the amplifier as the amplitude of the sine wave approaches the power supply rails. The oscillator is designed to have a small-signal loop gain greater than one. The higher gain allows an oscillator to start by
212:
In RC oscillator circuits which use a single inverting amplifying device, such as a transistor, tube, or an op amp with the feedback applied to the inverting input, the amplifier provides 180° of the phase shift, so the RC network must provide the other 180°. Since each capacitor can provide a
666:
slightest decrease will cause the sine wave to die out exponentially to zero. Therefore, all practical oscillators must have a nonlinear component in the feedback loop, to reduce the gain as the amplitude increases, leading to stable operation at the amplitude where the loop gain is unity.
208:
to compensate for the energy lost as the signal passes through the feedback network, to create sustained oscillations. As long as the gain of the amplifier is high enough that the total gain around the loop is unity or higher, the circuit will generally oscillate.
717:(thus decreasing the oscillator's output level). If the level is too low, the lamp cools down and increases the gain. The 1939 HP200A oscillator uses this technique. Modern variations may use explicit level detectors and gain-controlled amplifiers.
226:
given variable capacitor in an RC oscillator. For example, a variable capacitor that could be varied over a 9:1 capacitance range will give an RC oscillator a 9:1 frequency range, but in an LC oscillator it will give only a 3:1 range.
493:. Together, these circuits form a bridge which is tuned at the desired frequency of oscillation. The signal in the C-R-C branch of the Twin-T filter is advanced, in the R-C-R - delayed, so they may cancel one another for frequency
651:) subtracting a constant, and applying the difference to a multiplier that adjusts the loop gain around an inverter. Such circuits have a near-instant amplitude response to the constant input and extremely low distortion.
200:(the amplification around the feedback loop) is equal to one. The purpose of the feedback RC network is to provide the correct phase shift at the desired oscillating frequency so the loop has 360° phase shift, so the
639:
integrators in a feedback loop, one with the signal applied to the inverting input or two integrators and an invertor. The advantage of this circuit is that the sinusoidal outputs of the two op-amps are 90°
724:
Wien bridge oscillator with automatic gain control. Rb is a small incandescent lamp. Usually, R1 = R2 = R and C1 = C2 = C. In normal operation, Rb self heats to the point where its resistance is Rf/2.
363:
308:
417:
1159:
467:
1092:, p. 664, "Alternatively, an amplitude-controlled resistor or other passive nonlinear element may be included as part of the amplifier or in the frequency-determining network."
535:
625:
743:. In this circuit, two RC circuits are used, one with the RC components in series and one with the RC components in parallel. The Wien Bridge is often used in audio
561:
204:, after passing through the loop will be in phase with the sine wave at the beginning and reinforce it, resulting in positive feedback. The amplifier provides
751:
or a two section variable potentiometer (which is more easily obtained than a variable capacitor suitable for generation at low frequencies). The archetypical
1252:
1052:, p. 694, "As the signal amplitude increases, the active device will switch from active operation to the zero-gain regions of cutoff and saturation."
1377:
255:
the feedback network is three identical cascaded RC sections. In the simplest design the capacitors and resistors in each section have the same value
1166:
40:
485:
Another common design is the "Twin-T" oscillator as it uses two "T" RC circuits operated in parallel. One circuit is an R-C-R "T" which acts as a
422:
The feedback network has an attenuation of 1/29, so the op-amp must have a gain of 29 to give a loop gain of one for the circuit to oscillate
1080:, p. 664, "If gross nonlinear operation is permitted, the limiter will distort the signal and the output will be far from sinusoidal."
1257:
221:
element, to tune an RC oscillator over a wide range two or more resistors or capacitors must be varied in unison, requiring them to be
365:. Then at the oscillation frequency each RC section contributes 60° phase shift for a total of 180°. The oscillation frequency is
890:
659:
The
Barkhausen criterion mentioned above does not determine the amplitude of oscillation. An oscillator circuit with only
1272:
313:
258:
213:
maximum of 90° of phase shift, RC oscillators require at least two frequency-determining capacitors in the circuit (two
168:, another type of feedback oscillator, the LC oscillator is used, but at frequencies below 100 kHz the size of the
996:
958:
648:
371:
900:
58:
647:
It is possible to stabilize a quadrature oscillator by squaring the sine and cosine outputs, adding them together, (
921:
1438:
1152:
1138:
428:
1189:
816:
185:
973:
860:
496:
1402:
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689:, a system that keeps the gain roughly constant during the entire cycle is used. A common design uses an
1204:
1387:
1040:
in the small-signal region, the amplitude will build up until the limiter stabilizes the system...."
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833:
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152:, causing it to generate an oscillating sinusoidal voltage. They are used to produce lower
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36:
1027:
Strauss, Leonard (1970), "Almost
Sinusoidal Oscillations — the linear approximation",
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188:, which says that the circuit will only oscillate at frequencies for which the
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136:, with some of its output energy fed back into its input through a network of
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232:
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to an amplifier, and x>2, the amplifier becomes an oscillator. (Note:
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217:), and most have three or more, with a comparable number of resistors.
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644:(in quadrature). This is useful in some communication circuits.
229:
Some examples of common RC oscillator circuits are listed below:
1133:
752:
636:
133:
196:
is equal to 360° (2π radians) or a multiple of 360°, and the
953:. India: Pearson Education India. pp. 8.2–8.6, 8.11.
685:
So in oscillators that must produce a very low-distortion
682:
must have gain significantly above one to start reliably.
177:
RC oscillators do not have as good frequency stability as
1106:
Amplitude of
Oscillation—Part II, Automatic Gain Control
489:. The second circuit is a C-R-C "T" which operates as a
1016:, Technical Manuals, Dover, pp. 178–179, TM 11-690
739:
One of the most common gain-stabilized circuits is the
697:
in the feedback circuit. These oscillators exploit the
1117:
1011:
317:
262:
573:
543:
499:
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124:
oscillator; they consist of an amplifying device, a
946:
747:because it can be easily tuned using a two-section
358:{\displaystyle \scriptstyle C\;=\;C1\;=\;C2\;=\;C3}
303:{\displaystyle \scriptstyle R\;=\;R1\;=\;R2\;=\;R3}
31:
may be too technical for most readers to understand
974:Eric Coates, 2015, AF Sine Wave Oscillators, p. 10
778:"Application Report SLOA060: Sine-Wave Oscillator"
670:exponentially amplifying some ever-present noise.
619:
555:
529:
461:
411:
357:
302:
184:The frequency of oscillation is determined by the
861:"Oscillators Module 3 - AF Sine Wave Oscillators"
412:{\displaystyle f={\frac {1}{2\pi RC{\sqrt {6}}}}}
108:, for its frequency selective part is called an
1430:
1031:(second ed.), McGraw-Hill, pp. 663–720
755:audio oscillator is a Wien Bridge oscillator.
1160:
888:
775:
654:
96:. A linear oscillator circuit which uses an
947:Rao, B.; Rajeswari, K.; Pantulu, P. (2012).
882:
776:Mancini, Ron; Palmer, Richard (March 2001).
635:The quadrature oscillator uses two cascaded
1014:Basic Theory and Application of Transistors
984:
895:. New Age International. pp. 224–225.
892:Electronics (fundamentals And Applications)
708:of the lamp increases in proportion to its
462:{\displaystyle R_{\mathrm {fb} }=29\cdot R}
1174:
1167:
1153:
978:
916:
914:
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834:"Oscillators Module 1 - Oscillator Basics"
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677:The result of this gain averaging is some
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59:Learn how and when to remove this message
43:, without removing the technical details.
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164:and electronic musical instruments. At
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1066:Exponential limiting—bipolar transistor
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530:{\displaystyle f={\frac {1}{2\pi RC}}}
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41:make it understandable to non-experts
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649:Pythagorean trigonometric identity
441:
438:
84:output signal, are composed of an
14:
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1126:
1033:at page 661, "It follows that if
1233:Armstrong or Meissner oscillator
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1012:Department of the Army (1962) ,
160:, in such applications as audio
20:
1111:
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1190:Barkhausen stability criterion
991:. Elsevier. pp. 397–398.
988:Frequency of Self-Oscillations
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1:
808:Practical Oscillator Handbook
758:
620:{\displaystyle x=C2/C1=R1/R2}
120:RC oscillators are a type of
1403:Transmission-line oscillator
985:Groszkowski, Janusz (2013).
811:. Elsevier. pp. 49–53.
7:
1205:Nyquist stability criterion
1118:Department of the Army 1962
1029:Wave Generation and Shaping
950:Electronic Circuit Analysis
10:
1455:
1388:Opto-electronic oscillator
889:Chattopadhyay, D. (2006).
732:
655:Low distortion oscillators
563:; if it is connected as a
244:
1370:
1337:
1309:
1281:
1258:Meacham bridge oscillator
1223:
1182:
922:"RC Feedback Oscillators"
805:Gottlieb, Irving (1997).
1357:Pearson–Anson oscillator
236:A phase-shift oscillator
868:Learn About Electronics
838:Learn About Electronics
783:. Texas Instruments Inc
1439:Electronic oscillators
1339:Relaxation oscillators
1301:Wien bridge oscillator
1291:Phase-shift oscillator
1210:Oscillator phase noise
1176:Electronic oscillators
741:Wien bridge oscillator
735:Wien bridge oscillator
729:Wien bridge oscillator
725:
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463:
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253:phase-shift oscillator
247:Phase-shift oscillator
241:Phase-shift oscillator
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1383:Delay-line oscillator
859:Coates, Eric (2015).
832:Coates, Eric (2015).
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631:Quadrature oscillator
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92:selective element, a
75:electronic oscillator
1141:at Wikimedia Commons
1104:, pp. 706–713,
1064:, pp. 703–706,
926:Electronics tutorial
571:
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186:Barkhausen criterion
1408:Klystron oscillator
1398:Robinson oscillator
1347:Blocking oscillator
1243:Colpitts oscillator
1195:Harmonic oscillator
679:harmonic distortion
556:{\displaystyle x=2}
476:A twin-T oscillator
179:crystal oscillators
100:, a combination of
80:, which generate a
1329:Tri-tet oscillator
1311:Quartz oscillators
1253:Lampkin oscillator
1248:Hartley oscillator
1120:, pp. 179–180
749:variable capacitor
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1378:Cavity oscillator
1324:Pierce oscillator
1319:Butler oscillator
1296:Twin-T oscillator
1268:Vackář oscillator
1263:Seiler oscillator
1200:Leeson's equation
1137:Media related to
745:signal generators
691:incandescent lamp
565:negative feedback
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481:Twin-T oscillator
407:
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166:radio frequencies
162:signal generators
158:audio frequencies
150:positive feedback
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1102:Strauss 1970
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1215:Phase noise
710:temperature
192:around the
190:phase shift
154:frequencies
130:vacuum tube
116:Description
818:0080539386
787:August 12,
759:References
714:thermistor
699:resistance
695:thermistor
174:capacitors
146:RC network
142:capacitors
126:transistor
106:capacitors
98:RC network
82:sinusoidal
932:August 9,
874:August 7,
844:August 7,
687:sine wave
516:π
454:⋅
391:π
202:sine wave
198:loop gain
170:inductors
156:, mostly
138:resistors
102:resistors
90:frequency
86:amplifier
1433:Category
706:filament
703:tungsten
122:feedback
78:circuits
49:May 2021
251:In the
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1183:Theory
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753:HP200A
662:linear
637:op-amp
223:ganged
134:op-amp
94:filter
88:and a
72:Linear
1371:Other
864:(PDF)
781:(PDF)
701:of a
693:or a
215:poles
144:, an
132:, or
993:ISBN
955:ISBN
934:2015
897:ISBN
876:2015
846:2015
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310:and
206:gain
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