8/17/2019 Wien Bridge Oscillator Tutorial and Theory

1/4

LINKS

Ho me

Sit e Map

Sit e Search

Link Partners

Blogspot

Bo okstore

Co ntact Us

Calculators & Tools

PCB SoftwareTrac e WidthTrac e CurrentTrac e ResistancePCB Impedance

4 Band Resistor 5 Band Resistor Circuit Simulator Res istor TableIndu ctance CalcCoil InductanceParallel W iresImpedance MatchRF Unit Converter Coax ImpedanceTwisted Pair Crosstalk Calc

Scientific Calc

Search: Search Site

Electronics Tutorial about Wien Bridge Oscillators

Wien Bridge Oscillator Navigation

Tutorial: 5 of 6

--- Select a Tutorial Page ---

Go Res et

The Wien Bridge Oscillator

In the previous RC Oscillator tutorial we s aw that a number of resis tors and capacitors can beconnected together with an inverting am plifier to produce an os cillating circuit. One of the s imples t sinewave oscillators which uses a RC network in place of the conventional LC tuned tank circuit to producea si nusoidal output waveform, is the Wien Bridge Oscillator .

The Wien Bridge Oscillator is so called because the circuit is based on a frequency-selective form of the Whetstone bridge circuit. The Wien Bridge os cillator is a two-sta ge RC co upled amplifier circuit thathas good stability at its resonant frequency, low distortion and is very easy to tune making it a popular circuit as an audio frequency oscillator but the phase shift of the ou tput signal is considerably differentfrom the previous phas e shi ft RC Oscillator .

The Wi en Bridge O scillator uses a feedback circuit consisting of a series RC circuit connected with aparallel RC of the same component values producing a phase delay o r phase advance circuitdepending upon the frequency. At the resonant frequency ƒr the pha se s hift is 0 . Consider the circuitbelow.

RC Phase Shift Network

The above RC network consists of a series RC circuit connected to a parallel RC forming basically aHigh Pass Filter connected to a Low Pass Filter producing a very selective second-order

frequency dependant Band Pass Filter with a high Q factor at the selected frequency, ƒr .

At low frequencies the reactance of the seri es capacitor ( C1 ) is very high so acts like an open circuit andblocks any input signal at Vin . Therefore there is no output signal, Vout . At high frequencies, thereactance of the parallel capacitor, ( C2 ) is very low s o this parallel connected capacitor acts like a shortcircuit on the output so again there is no output signal. However, between these two extremes theoutput voltage reaches a maximum value with the frequency at which this happens being called theResonant Frequency , (ƒr ).

At this resonant frequency, the circuits reactance equals its res is tance as Xc = R so the phase shiftbetween the input and output equals zero degrees. The m agnitude of the output voltage is therefore atits m aximum and is equal to one third (1/3) of the input voltage as s hown.

Do you like our Site?Help us to Share It

2

Like 2.7k

Practical Oscillator Handbook

Irving M. Gottlieb...

Best Price £34.00 or Buy New £41.49

Priv acy Informatio n

o

http://www.eeweb.com/toolbox/twisted-pairhttp://www.eeweb.com/toolbox/rf-unit-converterhttp://www.eeweb.com/toolbox/l-matchhttp://www.eeweb.com/toolbox/coil-inductance/http://www.eeweb.com/toolbox/resistor-tableshttp://www.partsim.com/http://www.eeweb.com/toolbox/4-band-resistor-calculatorhttp://www.electronics-tutorials.ws/bookstore/bookstore.htmlhttp://www.electronics-tutorials.ws/blog/http://www.electronics-tutorials.ws/sitesearch.htmlhttp://www.electronics-tutorials.ws/sitemap/sitemap.htmlhttp://www.electronics-tutorials.ws/http://www.electronics-tutorials.ws/http://www.electronics-tutorials.ws/http://www.amazon.co.uk/gp/offer-listing/0750631023/ref=as_li_tf_til?tag=basicelecttut-21&camp=1406&creative=6394&linkCode=am1&creativeASIN=0750631023&adid=1CYFXCMAK1RWWQHKNXMZ&&ref-refURL=http%3A%2F%2Fwww.electronics-tutorials.ws%2Foscillator%2Fwien_bridge.htmlhttp://www.amazon.co.uk/gp/offer-listing/0750631023/ref=as_li_tf_til?tag=basicelecttut-21&camp=1406&creative=6394&linkCode=am1&creativeASIN=0750631023&adid=1CYFXCMAK1RWWQHKNXMZ&&ref-refURL=http%3A%2F%2Fwww.electronics-tutorials.ws%2Foscillator%2Fwien_bridge.htmlhttp://www.amazon.co.uk/gp/offer-listing/0750631023/ref=as_li_tf_til?tag=basicelecttut-21&camp=1406&creative=6394&linkCode=am1&creativeASIN=0750631023&adid=1CYFXCMAK1RWWQHKNXMZ&&ref-refURL=http%3A%2F%2Fwww.electronics-tutorials.ws%2Foscillator%2Fwien_bridge.htmlhttp://www.amazon.co.uk/dp/0750631023/ref=as_li_tf_til?tag=basicelecttut-21&camp=1406&creative=6394&linkCode=as1&creativeASIN=0750631023&adid=1CYFXCMAK1RWWQHKNXMZ&&ref-refURL=http%3A%2F%2Fwww.electronics-tutorials.ws%2Foscillator%2Fwien_bridge.htmlhttp://www.electronics-tutorials.ws/oscillator/rc_oscillator.htmlhttp://www.amazon.co.uk/dp/0750631023/ref=as_li_tf_til?tag=basicelecttut-21&camp=1406&creative=6394&linkCode=as1&creativeASIN=0750631023&adid=1CYFXCMAK1RWWQHKNXMZ&&ref-refURL=http%3A%2F%2Fwww.electronics-tutorials.ws%2Foscillator%2Fwien_bridge.htmlhttp://www.amazon.co.uk/dp/0750631023/ref=as_li_tf_til?tag=basicelecttut-21&camp=1406&creative=6394&linkCode=as1&creativeASIN=0750631023&adid=1CYFXCMAK1RWWQHKNXMZ&&ref-refURL=http%3A%2F%2Fwww.electronics-tutorials.ws%2Foscillator%2Fwien_bridge.htmlhttp://www.amazon.co.uk/dp/0750631023/ref=as_li_tf_til?tag=basicelecttut-21&camp=1406&creative=6394&linkCode=as1&creativeASIN=0750631023&adid=1CYFXCMAK1RWWQHKNXMZ&&ref-refURL=http%3A%2F%2Fwww.electronics-tutorials.ws%2Foscillator%2Fwien_bridge.htmlhttp://www.amazon.co.uk/dp/0750631023/ref=as_li_tf_til?tag=basicelecttut-21&camp=1406&creative=6394&linkCode=as1&creativeASIN=0750631023&adid=1CYFXCMAK1RWWQHKNXMZ&&ref-refURL=http%3A%2F%2Fwww.electronics-tutorials.ws%2Foscillator%2Fwien_bridge.htmlhttp://www.eeweb.com/toolbox/rf-unit-converterhttp://www.addthis.com/bookmark.php?v=250&pubid=ra-4dabe1c24a1ae8c8http://www.electronics-tutorials.ws/filter/filter_4.htmlhttp://www.electronics-tutorials.ws/filter/filter_2.htmlhttp://www.electronics-tutorials.ws/filter/filter_3.htmlhttp://www.electronics-tutorials.ws/oscillator/rc_oscillator.htmlhttp://www.eeweb.com/toolbox/calculatorhttp://www.eeweb.com/toolbox/microstrip-crosstalk/http://www.eeweb.com/toolbox/twisted-pairhttp://www.eeweb.com/toolbox/coaxhttp://www.eeweb.com/toolbox/rf-unit-converterhttp://www.eeweb.com/toolbox/l-matchhttp://www.eeweb.com/toolbox/parallel-wire-inductancehttp://www.eeweb.com/toolbox/coil-inductance/http://www.eeweb.com/toolbox/wire-inductancehttp://www.eeweb.com/toolbox/resistor-tableshttp://www.partsim.com/http://www.eeweb.com/toolbox/5-band-resistor-calculatorhttp://www.eeweb.com/toolbox/4-band-resistor-calculatorhttp://www.eeweb.com/toolbox/microstrip-impedancehttp://www.eeweb.com/toolbox/trace-resistancehttp://www.eeweb.com/toolbox/internal-pcb-trace-max-currenthttp://www.eeweb.com/toolbox/internal-pcb-trace-widthhttp://www.pcbweb.com/http://www.eeweb.com/toolboxhttp://www.pcbweb.com/registerhttp://www.electronics-tutorials.ws/http://rcm-uk.amazon.co.uk/e/cm/privacy-policy.html?o=2http://www.amazon.co.uk/gp/offer-listing/0750631023/ref=as_li_tf_til?tag=basicelecttut-21&camp=1406&creative=6394&linkCode=am1&creativeASIN=0750631023&adid=1CYFXCMAK1RWWQHKNXMZ&&ref-refURL=http%3A%2F%2Fwww.electronics-tutorials.ws%2Foscillator%2Fwien_bridge.htmlhttp://www.amazon.co.uk/dp/0750631023/ref=as_li_tf_til?tag=basicelecttut-21&camp=1406&creative=6394&linkCode=as1&creativeASIN=0750631023&adid=1CYFXCMAK1RWWQHKNXMZ&&ref-refURL=http%3A%2F%2Fwww.electronics-tutorials.ws%2Foscillator%2Fwien_bridge.htmlhttp://www.amazon.co.uk/dp/0750631023/ref=as_li_tf_til?tag=basicelecttut-21&camp=1406&creative=6394&linkCode=as1&creativeASIN=0750631023&adid=1CYFXCMAK1RWWQHKNXMZ&&ref-refURL=http%3A%2F%2Fwww.electronics-tutorials.ws%2Foscillator%2Fwien_bridge.htmlmailto:webmaster@electronics-tutorials.wshttp://www.electronics-tutorials.ws/bookstore/bookstore.htmlhttp://www.electronics-tutorials.ws/blog/http://www.electronics-tutorials.ws/links/links.htmlhttp://www.electronics-tutorials.ws/sitesearch.htmlhttp://www.electronics-tutorials.ws/sitemap/sitemap.htmlhttp://www.electronics-tutorials.ws/index.html

8/17/2019 Wien Bridge Oscillator Tutorial and Theory

2/4

Output Gain and Phase Shift

It can be seen that at very low frequencies the phase angle between the input and output signals is"Positive" (Phase Advanced), while at very high frequencies the phase angle becomes "Negative"(Phase Delay). In the middle of these two points the circuit is at its resonant frequency, ( ƒr ) with the twosignal s being "in-phas e" or 0 . We can therefore define this res onant frequency point with the followingexpression.

Resonant Freque ncy

Where:ƒr is the Res onant Frequency in HertzR is the Resi stance in Ohms

C is the Capacitance in Farads

Then this frequency selective RC network forms the basis of the Wien Bridge Oscillator circuit. If wenow place this RC network across a non-inverting amplifier which has a gain of 1+R1/R2 the followingoscillator circuit is produced.

Wien Bridge Oscillator

o

8/17/2019 Wien Bridge Oscillator Tutorial and Theory

3/4

The output of the operational amplifier is fed back to both the inputs of the amplifier. One part of thefeedback signal is connected to the inverting input terminal (negative feedback) via the resis tor divider network of R1 and R2 which allows the amplifiers voltage gain to be adjusted within narrow limits. Theother part is fed back to the non-inverting input terminal (positive feedback) via the RC Wien Bridgenetwork.

The RC network is connected in the positive feedback path of the amplifier and has zero phase shift a jus t one frequency. Then at the se lected res onant frequency, ( ƒr ) the voltages applied to the invertingand non-inverting inputs will be equal and "in-phase" so the positive feedback will cancel out thenegative feedback signal causing the circuit to oscill ate.

Also the voltage gain of the amplifier circuit MUST be equal to three "Gain = 3" for oscilla tions to s tart.This value is s et by the feedback resis tor network, R1 and R2 for an inverting amplifier and is given asthe ratio -R1/R2 . Also, due to the open-loop gain limitations of operational amplifiers, frequenciesabove 1MHz are unachievable without the us e of s pecial high frequency op-amps .

Wien Bridge Oscillator Summary

Then for oscillations to occur in a Wien Bridge Oscillator circuit the following conditions m ust apply.

1. With no input signal the Wien Bridge Oscillator produces output oscillations. 2. The Wien Bridge Oscillator can produce a large range of frequencies. 3. The Voltage gain of the amplifier m ust be at leas t 3. 4. The network can be used with a Non-inverting am plifier. 5. The input resistance of the amplifier must be high compared to R s o that the RC network isnot overloaded and alter the required conditions. 6. The output resistance of the amplifier must be low so that the effect of external loading isminimised. 7. Some method of s tabilizing the amplitude of the oscillations mus t be provided because if thevoltage gain of the amplifier is too small the desired oscillation will decay and stop and if it istoo large the output amplitude ris es to the value of the supply rails, which saturates the op-ampand causes the output waveform to become distorted. 8. With amplitude stabilisation in the form of feedback diodes, oscillations from the oscillator can go on indefinitely.

Example No1

Determine the maximum and minimum frequency of oscillations of a Wien Bridge Oscillator circuithaving a resistor of 10kΩ and a variable capacitor of 1nF to 1000nF .

The frequency of oscillations for a Wien Bridge Oscillator is given as:

Lowest Frequency

Highest Frequency

8/17/2019 Wien Bridge Oscillator Tutorial and Theory

4/4

Goto Page: 1 2 3 4 5 6

In our final look at Oscillators , we will examine the Crystal Oscillator which uses a quartz crystal asits tank circuit to produce a high frequency and very stable si nusoidal waveform.

Basic Electronics Tutorials by Wayne Storr. Last updated: May 2013 ,Copyright © 1999 − 2013, Electronics-Tutorials.w s, All Right Reserved.

| Privacy Policy | Terms of Use | Site Map | Contact Us | Basic Electronics Tutorials |

http://www.electronics-tutorials.ws/mailto:webmaster@electronics-tutorials.ws?subject=User%20Questionhttp://www.electronics-tutorials.ws/sitemap/sitemap.htmlhttp://www.electronics-tutorials.ws/terms.htmlhttp://www.electronics-tutorials.ws/privacypolicy.htmlhttp://www.electronics-tutorials.ws/http://www.electronics-tutorials.ws/oscillator/crystal.htmlhttp://www.electronics-tutorials.ws/oscillator/crystal.htmlhttp://www.electronics-tutorials.ws/oscillator/rc_oscillator.htmlhttp://www.electronics-tutorials.ws/oscillator/colpitts.htmlhttp://www.electronics-tutorials.ws/oscillator/hartley.htmlhttp://www.electronics-tutorials.ws/oscillator/oscillators.html