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university:courses:electronics:electronics-lab-13a [24 Jul 2017 15:40]
Antoniu Miclaus change amplitude value to peak-peak
university:courses:electronics:electronics-lab-13a [25 Oct 2017 05:20]
Trecia Agoylo
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 ===== Hardware Setup: ===== ===== Hardware Setup: =====
  
-The waveform generator, W1, should be configured for a 1 KHz sine wave with 6.0 volt amplitude peak amplitude and 0 offset. ​Channel one of the scope should be connected to display the output of the first generator and both scope channels 1 and 2 should be set to display 1V per division.+Channel one of the scope should be connected to display the output of the first generator and both scope channels 1 and 2 should be set to display 1V per division. ​The breadboard connections are shown in figure 2. 
 +{{ :​university:​courses:​electronics:​a13a_f2_bb.png?​ |}} 
 + 
 +<WRAP centeralign>​ Figure 2 Push - Pull Output stage Breadboard Circuit </​WRAP>​ 
  
 ===== Procedure: ===== ===== Procedure: =====
 +The waveform generator, W1, should be configured for a 1 KHz sine wave with 6.0 volt amplitude peak amplitude and 0 offset. Using scope channel 1 to observe the input at W1 and scope channel 2 to observe the output of the amplifier at R<​sub>​L</​sub>​.
 +{{ :​university:​courses:​electronics:​a13a_f3_wf.png?​ |}}
  
-Next, apply power and adjust the waveform generator so that W1 is a 100 Hz triangle wave with 0V offset and 3.0 V amplitude values. Use the oscilloscope in the x-y mode to observe the voltage-transfer curve of the circuit. Record the curve on paper, label all breakpoints,​ slopes, and saturation levels, and justify them in terms of circuit operation and given component values.+<WRAP centeralign>​ Figure ​Push Pull Output stage Waveforms </​WRAP>​
  
 +Next, apply power and adjust the waveform generator so that W1 is a 100 Hz triangle wave with 0V offset and 3.0 V amplitude values. Use the oscilloscope in the x-y mode to observe the voltage-transfer curve of the circuit. ​
 +
 +{{ :​university:​courses:​electronics:​a13a_f4_tc.png?​400 |}}
 +
 +<WRAP centeralign>​ Figure 4 Voltage-transfer curve </​WRAP>​
 +
 +===== Questions: =====
 +Record the curve on paper, label all breakpoints,​ slopes, and saturation levels, and justify them in terms of circuit operation and given component values.
 +
 Switch the scope to just the time display mode, and adjust the waveform generator so that W1 is a 1 kHz sine wave with the amplitude = 0 V. Switch the scope to just the time display mode, and adjust the waveform generator so that W1 is a 1 kHz sine wave with the amplitude = 0 V.
  
-• Starting with the amplitude = 0 V, gradually increase it until you just begin to see an signal on scope channel 2 appear at the output. For what range of amplitude values of W1 can we say that both BJT's are essentially off? Confirm this by observing the voltages of the current-sensing resistances R<​sub>​1</​sub>​ and R<​sub>​2</​sub>​.+• Starting with the amplitude = 0 V, gradually increase it until you just begin to see signal on scope channel 2 appear at the output. For what range of amplitude values of W1 can we say that both BJT's are essentially off? Confirm this by observing the voltages of the current-sensing resistances R<​sub>​1</​sub>​ and R<​sub>​2</​sub>​.
  
 • Raise W1 to 6.0V amplitude value, and record the amplitude of the output waveform as well as the collector currents of the BJTs, which can be found via Ohm's law from the voltages across R<​sub>​1</​sub>​ and R<​sub>​2</​sub>,​ and justify your findings in terms of circuit operation and the given component values. • Raise W1 to 6.0V amplitude value, and record the amplitude of the output waveform as well as the collector currents of the BJTs, which can be found via Ohm's law from the voltages across R<​sub>​1</​sub>​ and R<​sub>​2</​sub>,​ and justify your findings in terms of circuit operation and the given component values.
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 Simulate the circuit of figure 1 using QUCS, compare with your lab findings, and justify any differences. Simulate the circuit of figure 1 using QUCS, compare with your lab findings, and justify any differences.
- 
-===== Questions: ===== 
- 
-Add questions here: 
  
 ====== Reducing Output Distortion: ====== ====== Reducing Output Distortion: ======
  
 The large amount of distortion at the zero-crossings in the basic push-pull stage of figure 1 is a result of a dead zone when both the NPN and PNP emitter followers are off. The waveform'​s dead zone at the zero-crossings is dramatically reduced if we pre-bias the BJTs with two V<​sub>​BE</​sub>​ drops, as shown in figure 2. Here, the pre-bias function is provided by diode connected NPN Q<​sub>​1</​sub>​ and PNP Q<​sub>​3</​sub>​. Resistors R<​sub>​1</​sub>​ and R<​sub>​2</​sub>​ provide bias current and set the idle current that flows in the output devices Q<​sub>​2</​sub>​ and Q<​sub>​4</​sub>​. The large amount of distortion at the zero-crossings in the basic push-pull stage of figure 1 is a result of a dead zone when both the NPN and PNP emitter followers are off. The waveform'​s dead zone at the zero-crossings is dramatically reduced if we pre-bias the BJTs with two V<​sub>​BE</​sub>​ drops, as shown in figure 2. Here, the pre-bias function is provided by diode connected NPN Q<​sub>​1</​sub>​ and PNP Q<​sub>​3</​sub>​. Resistors R<​sub>​1</​sub>​ and R<​sub>​2</​sub>​ provide bias current and set the idle current that flows in the output devices Q<​sub>​2</​sub>​ and Q<​sub>​4</​sub>​.
- 
 ===== Directions: ===== ===== Directions: =====
  
-With the power turned off, assemble the circuit of figure ​2, keeping leads as short and neat as possible. NPN transistors Q<​sub>​1</​sub>​ and Q<​sub>​2</​sub>,​ PNP transistor Q<​sub>​3</​sub>​and Q<​sub>​4</​sub>​ should be selected from the available devices with the best matching of V<​sub>​BE</​sub>​. Transistors fabricated in the same package such as the SSM2212 or the CA3046 tend to match much better than individual devices.+With the power turned off, assemble the circuit of figure ​5, keeping leads as short and neat as possible. NPN transistors Q<​sub>​1</​sub>​ and Q<​sub>​2</​sub>,​ PNP transistor Q<​sub>​3</​sub>​and Q<​sub>​4</​sub>​ should be selected from the available devices with the best matching of V<​sub>​BE</​sub>​. Transistors fabricated in the same package such as the SSM2212 or the CA3046 tend to match much better than individual devices.
  
 {{ :​university:​courses:​electronics:​a13a_f2.png?​500 |}} {{ :​university:​courses:​electronics:​a13a_f2.png?​500 |}}
  
-<WRAP centeralign>​ Figure ​Push - pull output stage with zero-crossing distortion elimination. </​WRAP>​+<WRAP centeralign>​ Figure ​Push - Pull output stage with zero-crossing distortion elimination. </​WRAP>​
  
-If we examine, in figure ​2, the loop formed by the base emitter voltages of Q<​sub>​1</​sub>,​ Q<​sub>​2</​sub>,​ Q<​sub>​3</​sub>​ and Q<​sub>​4</​sub>​ we know that the sum of the voltage drops around the loop must sum to zero. Thus if Q<​sub>​1</​sub>​ is identical to Q<​sub>​2</​sub>​ and Q<​sub>​3</​sub>​ is identical to Q<​sub>​4</​sub>,​ the voltage around the loop will be zero only when the current in Q<​sub>​1</​sub>​ is identical to the current in Q<​sub>​2</​sub>​ and the current in Q<​sub>​3</​sub>​ is identical to the current in Q<​sub>​4</​sub>​. Thus when the output is at zero volts i.e. there is no current in R<​sub>​L</​sub>,​ the input must also be at zero volts.+If we examine, in figure ​5, the loop formed by the base emitter voltages of Q<​sub>​1</​sub>,​ Q<​sub>​2</​sub>,​ Q<​sub>​3</​sub>​ and Q<​sub>​4</​sub>​ we know that the sum of the voltage drops around the loop must sum to zero. Thus if Q<​sub>​1</​sub>​ is identical to Q<​sub>​2</​sub>​ and Q<​sub>​3</​sub>​ is identical to Q<​sub>​4</​sub>,​ the voltage around the loop will be zero only when the current in Q<​sub>​1</​sub>​ is identical to the current in Q<​sub>​2</​sub>​ and the current in Q<​sub>​3</​sub>​ is identical to the current in Q<​sub>​4</​sub>​. Thus when the output is at zero volts i.e. there is no current in R<​sub>​L</​sub>,​ the input must also be at zero volts. 
 +===== Hardware Setup: ===== 
 + 
 +Channel one of the scope should be connected to display the output of the first generator and both scope channels 1 and 2 should be set to display 1V per division. The breadboard connections are shown in figure 2. 
 +{{ :​university:​courses:​electronics:​a13a_f6_bb.png?​ |}} 
 + 
 +<WRAP centeralign>​ Figure 6 Push - Pull Output stage with zero-crossing distortion elimination Breadboard Circuit </​WRAP>​ 
 + 
 +===== Procedure: ===== 
 +The waveform generator, W1, should be configured for a 1 KHz sine wave with 6.0 volt amplitude peak amplitude and 0 offset. Using scope channel 1 to observe the input at W1 and scope channel 2 to observe the output of the amplifier at R<​sub>​L</​sub>​. 
 +{{ :​university:​courses:​electronics:​a13a_f7_wf.png?​ |}} 
 + 
 +<WRAP centeralign>​ Figure 7 Push - Pull Output stage with zero-crossing distortion elimination Waveforms </​WRAP>​
  
 ===== Questions: ===== ===== Questions: =====
  
-• Display the input / output transfer curve of the circuit of figure ​2, record it on paper, label all breakpoints,​ slopes, and saturation levels, and justify them in terms of circuit operation and the given component values.+• Display the input / output transfer curve of the circuit of figure ​5, record it on paper, label all breakpoints,​ slopes, and saturation levels, and justify them in terms of circuit operation and the given component values.
  
 • Apply a 1-kHz sine wave of 0 V offset and various amplitudes, and verify that the circuit yields Vout ? Vin all the way down to small amplitudes. What is the upper limit on the amplitude of W1 before the circuit starts to distort? Justify quantitatively in terms of the transfer curve just observed. • Apply a 1-kHz sine wave of 0 V offset and various amplitudes, and verify that the circuit yields Vout ? Vin all the way down to small amplitudes. What is the upper limit on the amplitude of W1 before the circuit starts to distort? Justify quantitatively in terms of the transfer curve just observed.
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 Measure the input impedance by inserting a 10K? resistor in series with the signal generator (between W1 and the emitters of Q<​sub>​1</​sub>​and Q<​sub>​3</​sub>​) and connecting the channel 1 differential scope inputs, 1+ , 1- across the 10K? resistor. Capture the input current vs. the input voltage and calculate the input resistance from the slope of the curve. Justify your results based on the component values used in the circuit. Measure the input impedance by inserting a 10K? resistor in series with the signal generator (between W1 and the emitters of Q<​sub>​1</​sub>​and Q<​sub>​3</​sub>​) and connecting the channel 1 differential scope inputs, 1+ , 1- across the 10K? resistor. Capture the input current vs. the input voltage and calculate the input resistance from the slope of the curve. Justify your results based on the component values used in the circuit.
  
-Simulate the circuit of figure ​using QUCS, compare with your lab findings, and justify any differences.+Simulate the circuit of figure ​using QUCS, compare with your lab findings, and justify any differences.
  
 ====== Another Configuration:​ ====== ====== Another Configuration:​ ======
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 {{ :​university:​courses:​electronics:​a13a_f3.png?​500 |}} {{ :​university:​courses:​electronics:​a13a_f3.png?​500 |}}
  
-<WRAP centeralign>​ Figure ​3 emitter follower ​zero-crossing distortion elimination </​WRAP>​+<WRAP centeralign>​ Figure ​8 Emitter Follower ​zero-crossing distortion elimination </​WRAP>​ 
 +===== Hardware Setup: ===== 
 + 
 +Channel one of the scope should be connected to display the output of the first generator and both scope channels 1 and 2 should be set to display 1V per division. The breadboard connections are shown in figure 2. 
 +{{ :​university:​courses:​electronics:​a13a_f9_bb.png?​ |}} 
 + 
 +<WRAP centeralign>​ Figure 9 Emitter Follower zero-crossing distortion elimination Breadboard Circuit </​WRAP>​ 
 + 
 +===== Procedure: ===== 
 +The waveform generator, W1, should be configured for a 1 KHz sine wave with 6.0 volt amplitude peak amplitude and 0 offset. Using scope channel 1 to observe the input at W1 and scope channel 2 to observe the output of the amplifier at R<​sub>​L</​sub>​. 
 +{{ :​university:​courses:​electronics:​a13a_f10_wf.png?​ |}} 
 + 
 +<WRAP centeralign>​ Figure 10 Emitter Follower zero-crossing distortion elimination Waveforms </​WRAP>​ 
  
 ===== Questions: ===== ===== Questions: =====
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 **Return to Lab Activity [[university:​courses:​electronics:​labs|Table of Contents]]** **Return to Lab Activity [[university:​courses:​electronics:​labs|Table of Contents]]**
 +
  
  
  
university/courses/electronics/electronics-lab-13a.txt · Last modified: 27 Jan 2021 22:36 by Robin Getz