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lab_electrical_engineering:6_opamps_2 [2026/06/17 11:00] – mexleadminlab_electrical_engineering:6_opamps_2 [2026/06/17 13:08] (current) – mexleadmin
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-=====Combination of Integrator and Schmitt Trigger - Oscillator===== +<wrap onlyprint>{{drawio>lab_electrical_engineering:namingtitle.svg}}</wrap>
- +
-====Background Information==== +
- +
-The circuits previously analyzed individually are now connected to form a complete system.\\  +
-The integrator and the Schmitt trigger together form an oscillator. The output signal +
-of the Schmitt trigger is fed back to the input of the integrator. Therefore, the output +
-signal simultaneously acts as the input signal of the overall system.\\ +
 \\  \\ 
-{{drawio>mexlefirst_intern:oscillator_overview.svg}} +====== Experiment 6: Operational Amplifier II - Pulse Width Modulation ====== 
-\\  +  * Circuits on the breadboard 
-\\  +  * Integrator 
-Due to this feedback, the circuit generates a periodic signal without requiring an external +  * Non-inverting Schmitt trigger 
-input signal, apart from the supply voltages of the operational amplifiers.\\  +  * Triangle–square-wave generator 
-\\  +  * Pulse-width modulation and control of a DC motor
-The Schmitt trigger generates a rectangular signal that is integrated into a triangular signal +
-until one of the switching thresholds is reached. At this point, the output state changes +
-and the process repeats continuously, producing a stable oscillation.\\  +
-\\  +
-When the circuit is first powered on, the oscillator starts due to small disturbances such +
-as noise, offset voltages of the operational amplifiers, or slight asymmetries in the circuit. +
-These small deviations move the system away from the unstable equilibrium point and initiate +
-the oscillation. +
  
-====Experimental Tasks==== +<wrap #challenge-description> 
-To analyze the behavior of the oscillator (triangle-rectangle generator), the following circuit is used:\\  +{{page>.:6_opamps_2:Challenge_description&nofooter}}
-\\  +
-<wrap left> +
-{{drawio>mexlefirst_intern:oscillator_circuit.svg}}+
 </wrap> </wrap>
-\\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\  \\ \\ \\ \\ \\ \\ \\ \\  
-\\  
-__Supply voltages (from power supply unit):__\\   
-UCC = + 3V, UEE = - 3V\\  
-\\  
-__Values of the components used:__\\  
-R1 = 200 kΩ, R1.3 = 10 kΩ, R2 = 20 kΩ, R3 = 27 kΩ, C1 = 10 nF\\ \\  
  
-  - Build the circuit on the MEXLE-board. R1 is a 200 kΩ potentiometer. Set it to a value of 200 kΩ. Perform the following measurements:  +<wrap #nuggets> 
-    * Connect channel 1 of the oscilloscope to TR and channel 2 to SQ. Switch on the power supply. +  {{page>Rectangular-to-Triangle_Signal_Conversion_(Integrator)&nofooter}} 
-    * Now try to generate a minimum and maximum frequency with your circuit by turning the potentiometer R1 to the left and right stops. Perform this experiment with two capacitance values: $C1=10~nF$ and $C1=1~nF$. Enter the measured frequency values in the following table.\\ \\ {{drawio>mexlefirst_intern:table_frequency_values_triangle_rectangle.svg}}\\ \\  +  {{page>Triangle-to-Rectangular_Conversion_(Schmitt_Trigger)&nofooter}} 
-  - Sketch the oscilloscope screen image at minimum and maximum frequency for the following capacitance values:\\ \\  $C1=10~nF$ and $C1=1~nF$.\\ \\ Label the lines with TR and SQ, respectively. Specify the oscilloscope settings you used. +  {{page>Combination_of_Integrator_and_Schmitt_Trigger_(Oscillator)&nofooter}} 
-\\  +  {{page>Duty_Cycle_Adjustment&nofooter}} 
- +  {{page>LED_Brightness_Control_using_PWM&nofooter}}
-**C1 = 10 nF, f = ƒmin**\\  +
-\\  +
-<wrap left> +
-{{drawio>mexlefirst_intern:oscilloscope_screen.svg}}+
 </wrap> </wrap>
-\\  
-\\  
-\\  
-Channel 1: $\frac {Volt}{Div}=$\\  
-\\  
-Channel 2: $\frac {Volt}{Div}=$\\  
-\\  
-\\  
-Time basis: $\frac {T}{Div}=$\\  
-\\  
-\\  
-\\  
-\\  
-\\  
-\\ 
-\\ \\ \\ \\  
-**C1 = 10 nF, f = ƒmax**\\  
-\\  
-<wrap left> 
-{{drawio>mexlefirst_intern:oscilloscope_screen.svg}} 
-</wrap> 
-\\  
-\\  
-\\  
-Channel 1: $\frac {Volt}{Div}=$\\  
-\\  
-Channel 2: $\frac {Volt}{Div}=$\\  
-\\  
-\\  
-Time basis: $\frac {T}{Div}=$\\  
-\\  
-\\  
-\\  
-\\  
-\\  
-\\  
-\\ \\ \\ \\  
-**C1 = 1 nF, f = ƒmin**\\  
-\\  
-<wrap left> 
-{{drawio>mexlefirst_intern:oscilloscope_screen.svg}} 
-</wrap> 
-\\  
-\\  
-\\  
-Channel 1: $\frac {Volt}{Div}=$\\  
-\\  
-Channel 2: $\frac {Volt}{Div}=$\\  
-\\  
-\\  
-Time basis: $\frac {T}{Div}=$\\  
-\\  
-\\  
-\\  
-\\  
-\\  
-\\  
-\\ \\ \\ \\  
-**C1 = 1 nF, f = ƒmax**\\  
-\\  
-<wrap left> 
-{{drawio>mexlefirst_intern:oscilloscope_screen.svg}} 
-</wrap> 
-\\  
-\\  
-\\  
-Channel 1: $\frac {Volt}{Div}=$\\  
-\\  
-Channel 2: $\frac {Volt}{Div}=$\\  
-\\  
-\\  
-Time basis: $\frac {T}{Div}=$\\  
-\\  
-\\  
-\\  
-\\  
-\\  
-\\  
-\\ \\ \\ \\  
-3. Explain how this circuit works in a few sentences.\\  
-\\  
-4. Why is it useful to use R1 as a potentiometer to vary the frequency rather than R2  
-or R3?\\  
-\\  
  
-====Test Questions====+===== Preparation =====
  
 +For this experiment, you should be able to apply and explain the following concepts:
 +  - "golden rules" for the negatively feedback, idealized operational amplifier
 +  - deviating properties of the real operational amplifier (e.g., output swing range, slew rate)
 +  - output-voltage waveform $U_A$ of the inverting integrator (inverting integrator) for different input voltages $U_E$, e.g.
 +    - DC voltage
 +    - square-wave voltage
 +    - arbitrary voltage waveform
 +  - integration time constant of the inverting integrator
 +  - Schmitt trigger
 +    - difference in feedback compared to the inverting integrator
 +    - idealized relationship between $U_E$ and $U_A$
 +    - idealized line diagram: $U_E$ and $U_A$ as a function of time
 +    - switching thresholds
 +    - threshold voltage
 +    - hysteresis
 +    - real behavior: output "in saturation"
 +  - structure of the triangle–square-wave generator