EE 3111 – Lab 3
Operational Amplifiers 2
Op Amps as Signal Generators
Today we will be building circuits that act as signal generators,
creating:
• Sine Waves
• Square Waves
• Triangle Waves
Oscillators
•
•
•
•
𝑓0 =
Wein Bridge Oscillator developed by Max Wein in 1891
First Implemented by William Hewlett in 1939
RC Op Amp circuit generates a sine wave
Has no input – self sustaining, with frequency of the sine
wave determined by values of Rs and Cs
1
2𝜋 𝑅1 𝑅2 𝐶1 𝐶2
• If C1 =C2, R1=R2
𝑓0 = 1�2𝜋𝜋𝜋
• Circuit requires that
𝑅4
1
=
𝑅4 + 𝑅3 3
Why?
Op Amps Circuits
Other Op Amp circuits can convert one waveform into another
(Inverting) Schmitt Trigger:
• Comparator or Thresholding circuit
• Vout Switches between
• -sat. if Vin >Vr
• +sat if Vin<-Vr
𝑅1 𝑉𝑠
𝑉𝑟 = −
𝑅1 + 𝑅2
• Has hysteresis, doesn’t switch at
Vin=0
• If Vin is triangle or sine wave, Vout is
square wave
Op Amps Circuits
(Inverting) Diffientiator
• 𝑉𝑜𝑜𝑜
𝑑
= −𝑅𝑅 𝑉𝑖𝑖
𝑑𝑑
(often RC=1)
• Very useful circuit in general, used in
analog signal processing and controls
• Turns a triangle wave into a square
wave (why?)
(Inverting) Integrator
• 𝑉𝑜𝑜𝑜
1 𝑡
=−
� 𝑉 𝑑𝑑
𝑅𝑅 0 𝑖𝑖
(often RC=1)
• Very useful circuit in general, used in
analog signal processing and controls
• Turns a square wave into a triangle
wave (why?)
Equipment Step by Step
Sync generator
and oscilloscope
• Read documents on Function Generator and Oscilloscope
• Sync the scope and func generator with BNC to BNC
• Don’t use gray cables (even though they are in this picture).
Use BNC to red and black clips
Scope and Func. Gen. Tips
• Measure voltage PP and
frequency via “quick measure”
• Autoscale is not always your
friend…
• Scope USB can save as images:
save/recall->save->new file…
• Set Symmetry to 50% for
triangle and square waves
• Can set frequency or period
• Can set max/min voltage or
amplitude + offset
• Instructions give waveforms in
period and max min
Scope and Func. Gen. Tips
• Need to use Freqlog.vi for
differentiator and integrator
• Need Scopegrab.vi to cut and
paste scope into Word
• Or use USB port on scope…
• VI’s are located in desktop/Labview VI’s/3111/
• Start labview 8.2 and load VI, don’t double-click VI file
• Select Oscilloscope and function generator address USB, make it
matches the label on the device.
• May need to turn device off and on, if windows message
appears, say “take no action”.
• Set function generator sweep parameters
Final Advice
• The oscillator circuit is very finicky, difficult to get good results
• I strongly suggest you work on the other three circuits first, as
they are fairly straightforward.
• Autoscale may miss the oscillator signal if there is noise. Try to
adjust the period and magnitude by hand. Also try single
captures to get the best wave form.
• Remember resistor in parallel with the feedback capacitor in
the Integrator.
• You should have 13 plots, and discuss each on briefly in your
lab report.
• Don’t use the gray scopes!