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Transcript
©IPK241001 NAME:...................................................................... DATE ISSUED:........................................................ COMPLETION DATE:............................................ FEEDBACK: SCHMITT TRIGGER PACKAGE (1). (2). (3). (4) The function of a Schmitt Trigger. The Inverting Schmitt Trigger. The Non-inverting Schmitt Trigger. Applications of Schmitt Triggers. 1 ©IPK241001 F(1). The function of Schmitt triggers. The aim of this assignment is to develop an understanding of the function of Schmitt triggers within electronic systems. Use the Support Booklet to complete the following tasks. 1). (a) What is the condition necessary for an op-amp comparator to give a saturated positive output voltage? ......................................................................................................................................... (b) What is the condition necessary for an op-amp comparator to give a saturated negative output voltage? ......................................................................................................................................... (c) What is likely to happen to the output of an op-amp comparator if the signal is noisy at the switching voltage? ......................................................................................................................................... ......................................................................................................................................... (d) Explain what is meant by the term hysteresis. ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... (e) Explain why a system with hysteresis will eliminate the problems caused by noise that a comparator suffers from. ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... (f) What type of feedback is needed to introduce hysteresis into an op-amp comparator circuit? ......................................................................................................................................... (g) How many different switching voltage levels are produced by hysteresis? ......................................................................................................................................... 2 ©IPK241001 F(2). The inverting Schmitt trigger. The aim of this assignment is to develop an understanding of the inverting op-amp Schmitt trigger circuit and to be able to calculate switching voltage levels. Use the Support Booklet to complete the following tasks. 1). (a) In the space below draw a labelled diagram of an inverting op-amp Schmitt trigger operating from a dual power supply. Label the feedback resistor Rf and the other resistor Ra. Use 0V as the reference voltage. (b) In terms of the voltages at the input terminals of the op-amp, state the conditions needed for:(i) the output of the op-amp to be saturated positively. ......................................................................................................................................... (ii) the output of the op-amp to be saturated negatively. ......................................................................................................................................... (c) Assume that the power supply voltages for the op-amp are +Vs and that the op-amp output saturates at the supply voltages. Calculate the formula for the voltage at the non-inverting input of the op-amp when:(i) the output of the op-amp is saturated positively. ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... (ii) the output of the op-amp is saturated negatively. ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... 3 ©IPK241001 (d) Suggest a formula for the switching voltages for the inverting op-amp Schmitt trigger. ......................................................................................................................................... (e) An inverting op-amp Schmitt trigger operates from a + 15V supply and has a reference voltage of 0V. Assuming that the op-amp output saturates at the supply voltages, calculate the switching voltage levels when:(i) Rf = 10k and Ra = 10k. ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... (ii) Rf = 10k and Ra = 1k. ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... (iii) Rf = 1k and Ra = 10k. ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... (f) For the values in (e)(i) above draw a sketch graph on the axes below to show how the output voltage varies as the input voltages changes from -15V to +15V and back again to -15V. output voltage +15V –15V +15V input voltage –15V 4 ©IPK241001 (g) An inverting op-amp Schmitt trigger operates from a + 15V supply and has a reference voltage of 0V. Assuming that the op-amp output saturates at the supply voltages and that Rf is 100k, calculate a value for Ra so that the switching voltages are:(i) +5V ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... (ii) +1V ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... (iii) +10V ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... (h) The circuit below shows a Schmitt trigger circuit operating from a single power supply of 12V. +12V Ra _ + Rf Vin Vout Ra ©ikes1001 (i) 0V What is the voltage at the positive input terminal of the op-amp when the output voltage is 0V. ......................................................................................................................................... ......................................................................................................................................... 5 ©IPK241001 ......................................................................................................................................... (ii) What is the voltage at the positive input terminal of the op-amp when the output voltage is +12V. ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... (iii) What are the switching voltage levels for this circuit? ......................................................................................................................................... (i) Calculate the switching voltage levels for the circuit below. +15V 15k _ + 100k Vin Vout 10k ©ikes1001 0V ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... 6 ©IPK241001 F(3). The non-inverting Schmitt trigger. The aim of this assignment is to develop an understanding of the non-inverting op-amp Schmitt trigger circuit and to be able to calculate switching voltage levels. Use the Support Booklet to complete the following tasks. 1). (a) In the space below draw a labelled diagram of a non-inverting op-amp Schmitt trigger operating from a dual power supply. Label the feedback resistor Rf and the other resistor Ra. Use 0V as the reference voltage. (b) In terms of the voltages at the input terminals of the op-amp, state the conditions needed for:(i) the output of the op-amp to be saturated positively. ......................................................................................................................................... (ii) the output of the op-amp to be saturated negatively. ......................................................................................................................................... (c) Assume that the power supply voltages for the op-amp are +Vs and that the op-amp output saturates at the supply voltages. If the input voltage is Vin, calculate the formula for the voltage at the non-inverting input of the op-amp when:(i) the output of the op-amp is saturated positively. ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... (ii) the output of the op-amp is saturated negatively. ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... 7 ©IPK241001 (d) Suggest a formula for the switching voltages for the non-inverting op-amp Schmitt trigger with the reference voltage as 0V. ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... (e) An non-inverting op-amp Schmitt trigger operates from a + 15V supply and has 0V as the reference voltage. Assuming that the op-amp output saturates at the supply voltages, calculate the switching voltage levels when:(i) Rf = 100k and Ra = 10k. ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... (ii) Rf = 100k and Ra = 1k. ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... (iii) Rf = 100k and Ra = 100. ......................................................................................................................................... ......................................................................................................................................... (f) For the values in (e)(i) above draw a sketch graph on the axes below to show how the output voltage varies as the input voltages changes from -15V to +15V and back again to -15V. output voltage +15V –15V +15V input voltage –15V 8 ©IPK241001 (g) An non-inverting op-amp Schmitt trigger operates from a + 15V supply and has a reference voltage of 0V. Assuming that the op-amp output saturates at the supply voltages and that Rf is 100k, calculate a value for Ra so that the switching voltages are:(i) +5V ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... (ii) +1V ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... (iii) +10V ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... (h) The circuit below shows a Schmitt trigger circuit operating from a single power supply of 12V. +12V Ra _ + Ra Rf Vin Vout Ra ©ikes1001 (i) 0V What is the voltage at the negative input terminal of the op-amp? ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... 9 ©IPK241001 (ii) What must be the voltage at the positive input terminal of the op-amp when the output voltage just switches to +12V? ......................................................................................................................................... (iii) What must be the voltage at the positive input terminal of the op-amp when the output voltage just switches to 0V? ......................................................................................................................................... (iii) What are the switching voltage levels for this circuit in terms of Ra and Rf? ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... (i) Calculate the switching voltage levels for the circuit below. +15V 15k _ + 10k 100k Vin Vout 10k ©ikes1001 0V ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... 10 ©IPK241001 F(4). Applications of Schmitt triggers. The aim of this assignment is to develop an understanding of the uses and applications of Schmitt trigger circuits. Use the Control Module Support Booklet to complete the following tasks. 1). (a) Using diagrams to help you, explain how a Schmitt trigger can be used to restore a logic signal that has become attenuated and noisy. .................................................................................................. .................................................................................................. .................................................................................................. .................................................................................................. .................................................................................................. .................................................................................................. .................................................................................................. .................................................................................................. .................................................................................................. .................................................................................................. .................................................................................................. .................................................................................................. (b) Explain why a Schmitt trigger is much better for this application than a comparator. .................................................................................................. .................................................................................................. .................................................................................................. .................................................................................................. .................................................................................................. .................................................................................................. .................................................................................................. .................................................................................................. 11 ©IPK241001 2). (a) Using diagrams to help you, explain how a Schmitt trigger can be used to convert a sine wave or triangular wave form into a pulse waveform. .................................................................................................. .................................................................................................. .................................................................................................. .................................................................................................. .................................................................................................. .................................................................................................. .................................................................................................. .................................................................................................. .................................................................................................. .................................................................................................. .................................................................................................. (b) Explain what differences would be noticed in the waveform if a comparator had been used instead of a Schmitt trigger. .................................................................................................. .................................................................................................. .................................................................................................. .................................................................................................. .................................................................................................. .................................................................................................. .................................................................................................. .................................................................................................. .................................................................................................. .................................................................................................. .................................................................................................. 12 ©IPK241001 3). (a) Draw a circuit diagram to show how a Schmitt trigger can be used as an astable oscillator. (b) Explain how the astable operates. ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... (c) What factors determine the frequency of operation. ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... 13 ©IPK241001 4). (a) Draw the circuit diagram of an inverting Schmitt trigger and add component values so that it is referenced to 0V, operates from +15V, and has switching levels of +1V. (b) Draw a layout for your circuit on the diagram below. 1 5 10 15 20 25 A B C D E A B C D E F G H I J F G H I J 1 5 10 15 20 25 ©ikes1001 (c) Construct your circuit onto protoboard and check that it works. (d) Connect the input to a function generator set to a triangle waveform at a frequency of 1kHz. Use an oscilloscope to monitor the input and output waveforms. Vary the amplitude of the input and describe the effect on the output. ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... 14 ©IPK241001 ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... (e) Suggest what would happen to the output if the reference voltage were varied. ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... (f) Test your theory and describe the effects. ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... 15 ©IPK241001 5). (a) Draw the circuit diagram of a Schmitt trigger astable with 0V as the reference voltage and switching voltages of +7.5V, operating from a 15V supply. (b) Show on the diagram below how you would construct a Schmitt astable. 1 5 10 15 20 25 A B C D E A B C D E F G H I J F G H I J 1 5 10 15 20 25 ©ikes1001 (c) Construct the astable and use 100k resistor and 100nF capacitor. (d) Use an oscilloscope to examine the output waveform and the waveform of the input to the Schmitt trigger. Describe their appearance. ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... 16 ©IPK241001 (e) Draw the waveforms on the diagram below. (f) Describe how the output waveform changes if the switching voltage level resistors are changed. ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... 17
