=====Triangle-to-Rectangular Conversion - Schmitt Trigger===== ====Background Information==== The operation of an OPV in the saturation range can be enforced in the circuit by feeding back the output signal, i.e., returning it to the non-inverting input (+ input). In the circuit shown, the feedback is provided by resistor $R_\mathrm{2}$.\\ \\ {{drawio>mexlefirst_public:non_inverting_schmitt_trigger_circuit.svg}} \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ The output voltage $u_\mathrm{a}$ can only take two values, either $\mathrm{+}U_\mathrm{sat}$ or $\mathrm{-}U_\mathrm{sat}$. It switches between these two values when no voltage drops at the differential input of the OPV, ($u_\mathrm{d}=0$). Then $i_\mathrm{R2}=\frac{u_\mathrm{a}}{R_\mathrm{2}}$ and $u_\mathrm{e}=-R_\mathrm{1} \cdot i_\mathrm{R1}$. Since the OPV input current is $i_\mathrm{p}=0$, the currents through the resistors must be equal, and the following relationship applies for the switching points: $u_\mathrm{e}=-\frac{R_\mathrm{1}}{R_\mathrm{2}}\cdot u_\mathrm{a}=\mp\frac{R_\mathrm{1}}{R_\mathrm{2}}\cdot U_\mathrm{sat}$ \\ \\ \\ {{drawio>mexlefirst_public:non_inverting_schmitt_trigger_characteristic_input_output_signal.svg}} \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ The image shows the input/output characteristic curve of the circuit known as a “non-inverting Schmitt trigger.” The reaction to any input signal is shown on the right. The circuit only switches to $\mathrm{+}U_\mathrm{sat}$, when the positive switching threshold at the input is reached. It only switches to $\mathrm{-}U_\mathrm{sat}$, when the negative switching threshold at the input is reached. ====Experimental Tasks==== To analyze the behavior of the schmitt trigger, the following circuit is used:\\ \\ {{drawio>mexlefirst_public:schmitt_trigger_circuit_experiment.svg}} \\ \\ \\ Supply voltages (from power supply unit):\\ UCC = + 3V, UEE = - 3V\\ \\ Values of the components used:\\ R2 = 20kΩ, R3 = 27kΩ\\ \\ \\ \\ \\ \\ \\ \\ \\ \\ - Calculate the switching thresholds using the given values. - Roughly sketch the voltage curves that you expect at the SQ output when you apply a triangular signal to Ue whose amplitude just reaches the switching points. \\ \\ **Output SQ**\\ \\ {{drawio>mexlefirst_public:oscilloscope_screen.svg}}\\ \\ \\ Channel 1:$\frac {Volt}{Div}=$\\ \\ \\ Time basis: $\frac {T}{Div}=$\\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ - Set up the Schmitt Trigger on the MEXLE-Board. **Please use the level shifting circuit at the input of the circuit.** Perform the following measurements on the Schmitt Trigger: * Connect channel 1 on the oscilloscope to 𝑈𝑒 and channel 2 to SQ. * Connect the function generator to the Ue input. Set it to triangle with a frequency of 1kHz and a voltage of 3 V (amplitude). * Sketch the oscilloscope screen image. \\ \\ **Ue = 3 V (amplitude), f = 1 kHz**\\ \\ {{drawio>mexlefirst_public:oscilloscope_screen.svg}}\\ \\ \\ Channel 1: $\frac {Volt}{Div}=$\\ \\ Channel 2: $\frac {Volt}{Div}=$\\ \\ \\ Time basis: $\frac {T}{Div}=$\\ \\ \\ \\ \\ \\ \\ \\ \\ - Sketch the oscilloscope screen image you would expect for 1 V (amplitude). \\ \\ **Ue = 1 V (amplitude), f = 1 kHz**\\ \\ {{drawio>mexlefirst_public:oscilloscope_screen.svg}}\\ \\ \\ Channel 1: $\frac {Volt}{Div}=$\\ \\ Channel 2: $\frac {Volt}{Div}=$\\ \\ \\ Time basis: $\frac {T}{Div}=$\\ \\ \\ \\ \\ \\ \\ \\ \\ - Compare your measurements with the calculation from sub-task 1 and the forecast from 2. Explain the results. ====Test Questions - Schmitt Trigger====