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university:courses:electronics:electronics-lab-4 [23 Mar 2017 15:53]
Doug Mercer [Directions and Setup:]
university:courses:electronics:electronics-lab-4 [26 Jan 2021 15:32]
Doug Mercer [For further reading on the Howland current source:]
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-====== Activity ​4. A BJT Curve Tracer ======+====== ActivityA BJT Curve Tracer ======
  
 ===== Objective: ===== ===== Objective: =====
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 ===== Background: ===== ===== Background: =====
  
-The variable analog outputs supplied by the Discovery ​hardware are voltages. The BJT collector current is controlled by the base current. The AWG output voltage must be converted into a suitable current to drive the base terminal of the device under investigation. A simple resistor can be used to convert a voltage into a current, as shown in figure 1. However, only if the voltage across the resistor is known or controlled in some way. In this simple circuit, the base current I<​sub>​B</​sub>​ = (V<​sub>​AWG1</​sub>​ - V<​sub>​BE</​sub>​)/​100KΩ. We can set V<​sub>​AWG1</​sub>​ to known values but we don’t know the exact value of V<​sub>​BE</​sub>​. We can of course remove an estimate of the V<​sub>​BE</​sub>​ mathematically. This is still only an estimate.+The variable analog outputs supplied by the ADALM2000 ​hardware are voltages. The BJT collector current is controlled by the base current. The AWG output voltage must be converted into a suitable current to drive the base terminal of the device under investigation. A simple resistor can be used to convert a voltage into a current, as shown in figure 1. However, only if the voltage across the resistor is known or controlled in some way. In this simple circuit, the base current I<​sub>​B</​sub>​ = (V<​sub>​AWG1</​sub>​ - V<​sub>​BE</​sub>​)/​100KΩ. We can set V<​sub>​AWG1</​sub>​ to known values but we don’t know the exact value of V<​sub>​BE</​sub>​. We can of course remove an estimate of the V<​sub>​BE</​sub>​ mathematically. This is still only an estimate.
  
 {{ :​university:​courses:​electronics:​a4_f1.png?​500 |}} {{ :​university:​courses:​electronics:​a4_f1.png?​500 |}}
  
-<WRAP centeralign>​ Figure 1 Simple I<​sub>​C</​sub>​ vs V<​sub>​CE</​sub>​ circuit </​WRAP>​+<WRAP centeralign>​ Figure 1Simple I<​sub>​C</​sub>​ vs V<​sub>​CE</​sub>​ circuit ​</​WRAP>​ 
 + 
 +{{ :​university:​courses:​electronics:​a4_nf1.png?​|}} 
 + 
 +<WRAP centeralign>​ Figure 2, Simple I<​sub>​C</​sub>​ vs V<​sub>​CE</​sub>​ circuit breadboard connection ​</​WRAP>​
  
 ===== Materials: ===== ===== Materials: =====
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 ===== Directions and Setup: ===== ===== Directions and Setup: =====
  
-Build the simple curve tracer circuit shown in figure ​1. The green boxes indicate where to connect the ADALM2000. Using the custom waveform editor in the Scopy AWG tool, construct a stair-step waveform with 5 levels. Be sure to reset so that you are starting with flat line at 0%. First set the type to constant. Then with start set to 0%, length set to 20% and offset set to -100% click on generate function. There should now be a line at -100% from 0 to 20%. Next change ​the start to 20% and the offset to -50% and then click on generate function again. There should now be a line at -50% from 20% to 40%. Next set the offset to +50% and the start to 60% and then click on generate function again. There should now be a line at 0% from 40% to 60% and a line at 50% from 60% to 80%. Finally set the offset to 100% and start to 80% and click on generate function one last time. There should now be a final line at 100% from 80% to 100%. Click on save and your new waveform should be in channel 2. Now at this point set the frequency to 40Hz, the amplitude to 2 V and the offset to 2.6 V. The waveform in the display should start at 0.6V and increase in 1 V increments to 4.6 V (0.6, 1.6, 2.6, 3.6, 4.6) Each step should ​be 5 mSec long for a total of 25 mSec. In AWG channel ​1 configure a triangle wave with an amplitude of 2.5 V and an offset of 2.5V (wave should swing from 0 to 5V). Set the frequency to 200 Hz ( 5 times the 40 Hz of channel 2). Comparing the waveforms in channel ​1 and channel ​2, the triangle wave in channel ​1 should go through one cycle from 0 to 5 V and back to zero during the time of one step in the waveform in channel ​2. It will probably be necessary to set the phase of channel ​1 to 270 degrees to make them line up in this way.+Build the simple curve tracer circuit shown in Figure ​1. The green boxes indicate where to connect the ADALM2000. Using the Scopy Signal Generator ​tool, in Channel 2  Buffer tab import ​the csv file for the stairstep signal needed. 
 +Now at this point set the amplitude to 2 V peak-to-peak ​and the offset to 2.6 V. The waveform in the display should start at 0.6V and increase in 1 V increments to 4.6 V (0.6, 1.6, 2.6, 3.6, 4.6). For each step to be 5 mSec long for a total of 25 mSec, set the sampling rate 200 Hz. 
 +In Signal Generator Channel ​1 configure a triangle wave with an amplitude of 5V peak-to-peak ​and an offset of 2.5V (wave should swing from 0 to 5V). Set the frequency to 200 Hz ( 5 times the 40 Hz of channel 2). Comparing the waveforms in Channel ​1 and Channel ​2, the triangle wave in Channel ​1 should go through one cycle from 0 to 5 V and back to zero during the time of one step in the waveform in Channel ​2. It will probably be necessary to set the phase of Channel ​1 to 90 degrees to make them line up in this way. 
  
-You should export your newly created stair-step waveform to a .csv file for future use. 
  
 ===== Procedure: ===== ===== Procedure: =====
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 {{ :​university:​courses:​electronics:​a4_f2.png?​500 |}} {{ :​university:​courses:​electronics:​a4_f2.png?​500 |}}
  
-<WRAP centeralign>​ Figure ​Circuit to generate a Gummel Plot </​WRAP>​+<WRAP centeralign>​ Figure ​3, Circuit to generate a Gummel Plot </​WRAP>​ 
 + 
 +{{ :​university:​courses:​electronics:​a4_nf2.png?​|}} 
 + 
 +<WRAP centeralign>​ Figure 4, Circuit to generate a Gummel Plot breadboard connection </​WRAP>​\\
  
 {{ :​university:​courses:​electronics:​a4_f3.jpg?​400 |}} {{ :​university:​courses:​electronics:​a4_f3.jpg?​400 |}}
  
-<WRAP centeralign>​ Figure ​Example Gummel Plot </​WRAP>​+<WRAP centeralign>​ Figure ​5, Example Gummel Plot </​WRAP>​
  
 (From: http://​www.synopsys.com/​Tools/​TCAD/​Pages/​hbtprocessing.aspx) (From: http://​www.synopsys.com/​Tools/​TCAD/​Pages/​hbtprocessing.aspx)
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 ===== Objective: ===== ===== Objective: =====
  
-We need to somehow remove V<​sub>​BE</​sub>​ from the equation in figure 1 which sets I<​sub>​B</​sub>​. The circuits shown in figures ​and perform the function to force V<​sub>​AWG1</​sub>​ across the 10KΩ resistor independent of the value of V<​sub>​BE</​sub>​.+We need to somehow remove V<​sub>​BE</​sub>​ from the equation in figure 1 which sets I<​sub>​B</​sub>​. The circuits shown in figures ​and perform the function to force V<​sub>​AWG1</​sub>​ across the 10KΩ resistor independent of the value of V<​sub>​BE</​sub>​.
  
 ===== Materials: ===== ===== Materials: =====
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 ===== Directions and Setup: ===== ===== Directions and Setup: =====
  
-Below are schematics for both a common emitter and a common base BJT curve tracer test circuit for use with the ADALM2000. It uses one dual opamp (ADTL082) powered from the +/- 5 Volt board supplies. In the common emitter configuration,​ one opamp serves as a virtual ground at the base terminal to convert the voltage steps from waveform generator W2 into base current steps through a 10KΩ resistor. The collector voltage is swept using a ramp from generator W1. V<​sub>​CE</​sub>​ is measured differentially by scope inputs 1+, 1-. The collector current, I<​sub>​C</​sub>​ is measured by scope inputs 2+, 2- differentially across a 100Ω resistor. A ratio of 100 for the base and collector resistors is used because beta, the collector current to base current gain, is often approximately 100. The voltage on the base terminal can be offset to either +2.5V or -2.5V (or 0V) to increase the possible V<​sub>​CE</​sub>​ swing (by -2.5 for NPN or +2.5 for PNP). The +2.5V is generated by a voltage divider from the +5V supply and the -2.5V is generated by inverting the +2.5V with the second opamp in the dual op-amp (ADTL082). The base and emitter connection can be interchanged to configure the device under test (DUT) in the common base mode. The resistor values are changed to 1KΩ for both in this configuration. This ratio of one is appropriate given that alpha, the ratio of emitter current to collector current, is very close to one. The voltage from W2 now sets the emitter current and the ramp on W1 sweeps the V<​sub>​CB</​sub>​ and is measured differentially with 1+, 1-.  The collector current I<​sub>​C</​sub>​ is measured differentially across the 1KΩ resistor with 2+, 2-. +Below are schematics for both a common emitter and a common base BJT curve tracer test circuit for use with the ADALM2000. It uses one dual opamp (ADTL082) powered from the +/- 5 Volt board supplies. In the common emitter configuration,​ one opamp serves as a virtual ground at the base terminal to convert the voltage steps from waveform generator W2 into base current steps through a 10KΩ resistor. The collector voltage is swept using a ramp from generator W1. V<​sub>​CE</​sub>​ is measured differentially by scope inputs 1+, 1-. The collector current, I<​sub>​C</​sub>​ is measured by scope inputs 2+, 2- differentially across a 100Ω resistor. A ratio of 100 for the base and collector resistors is used because beta, the collector current to base current gain, is often approximately 100. The voltage on the base terminal can be offset to either +2.5V or -2.5V (or 0V) to increase the possible V<​sub>​CE</​sub>​ swing (by -2.5 for NPN or +2.5 for PNP). The +2.5V is generated by a voltage divider from the +5V supply and the -2.5V is generated by inverting the +2.5V with the second opamp in the dual op-amp (ADTL082). The base and emitter connection can be interchanged to configure the device under test (DUT) in the common base mode. The resistor values are changed to 1KΩ for both in this configuration. This ratio of one is appropriate given that alpha, the ratio of emitter current to collector current, is very close to one. The voltage from W2 now sets the emitter current and the ramp on W1 sweeps the V<​sub>​CB</​sub>​ and is measured differentially with 1+, 1-.  The collector current I<​sub>​C</​sub>​ is measured differentially across the 1KΩ resistor with 2+, 2-. 
  
 {{ :​university:​courses:​electronics:​a4_f4.png?​500 |}} {{ :​university:​courses:​electronics:​a4_f4.png?​500 |}}
  
-<WRAP centeralign>​ Figure ​4, Common Emitter configuration </​WRAP>​+<WRAP centeralign>​ Figure ​6, Common Emitter configuration ​</​WRAP>​ 
 + 
 +{{ :​university:​courses:​electronics:​a4_nf4.png?​|}} 
 + 
 +<WRAP centeralign>​ Figure 7, Common Emitter configuration breadboard connection ​</​WRAP>​
  
 {{ :​university:​courses:​electronics:​a4_f5.png?​500 |}} {{ :​university:​courses:​electronics:​a4_f5.png?​500 |}}
  
-<WRAP centeralign>​ Figure ​5, Common Base configuration </​WRAP>​+<WRAP centeralign>​ Figure ​8, Common Base configuration </​WRAP>​
  
-The following characteristic curves where taken using various NPN and PNP transistors in the common emitter configuration.  A 10KΩ base resistor and 100Ω collector resistor was used in both cases.+{{ :​university:​courses:​electronics:​a4_nf5.png?​|}} 
 + 
 +<WRAP centeralign>​ Figure 9, Common Base configuration breadboard connection </​WRAP>​ 
 + 
 +The following characteristic curves where taken using various NPN and PNP transistors in the common emitter configuration. ​ A 10KΩ base resistor and 100Ω collector resistor was used in both cases.
  
 {{ :​university:​courses:​electronics:​a4_f6.png?​500 |}} {{ :​university:​courses:​electronics:​a4_f6.png?​500 |}}
  
-<WRAP centeralign>​ Figure ​NPN I<​sub>​C</​sub>​ vs. V<​sub>​CE</​sub>​ </​WRAP>​+<WRAP centeralign>​ Figure ​10, NPN I<​sub>​C</​sub>​ vs. V<​sub>​CE</​sub>​ </​WRAP>​
  
 NPN, beta is approximately 166. NPN, beta is approximately 166.
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 {{ :​university:​courses:​electronics:​a4_f7.png?​500 |}} {{ :​university:​courses:​electronics:​a4_f7.png?​500 |}}
  
-<WRAP centeralign>​ Figure ​PNP I<​sub>​C</​sub>​ vs. V<​sub>​CE</​sub>​ </​WRAP>​+<WRAP centeralign>​ Figure ​11, PNP I<​sub>​C</​sub>​ vs. V<​sub>​CE</​sub>​ </​WRAP>​
  
 PNP, beta is approximately 200. PNP, beta is approximately 200.
  
-The following characteristic curves where taken using the same NPN and PNP transistors in the common base configuration.  A 1KΩ emitter resistor and 1KΩ collector resistor was used in both cases+The following characteristic curves where taken using the same NPN and PNP transistors in the common base configuration. ​ A 1KΩ emitter resistor and 1KΩ collector resistor was used in both cases
  
 {{ :​university:​courses:​electronics:​a4_f8.png?​500 |}} {{ :​university:​courses:​electronics:​a4_f8.png?​500 |}}
  
-<WRAP centeralign>​ Figure ​NPN I<​sub>​C</​sub>​ vs. V<​sub>​CB</​sub>​ </​WRAP>​+<WRAP centeralign>​ Figure ​12, NPN I<​sub>​C</​sub>​ vs. V<​sub>​CB</​sub>​ </​WRAP>​
  
 {{ :​university:​courses:​electronics:​a4_f9.png?​500 |}} {{ :​university:​courses:​electronics:​a4_f9.png?​500 |}}
  
-<WRAP centeralign>​ Figure ​PNP I<​sub>​C</​sub>​ vs. V<​sub>​CB</​sub>​ </​WRAP>​+<WRAP centeralign>​ Figure ​13, PNP I<​sub>​C</​sub>​ vs. V<​sub>​CB</​sub>​ </​WRAP>​
  
 Further reading: http://​en.wikipedia.org/​wiki/​Transistor_curve_tracer Further reading: http://​en.wikipedia.org/​wiki/​Transistor_curve_tracer
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 ===== Directions: ===== ===== Directions: =====
  
-The circuit below, figure ​8, can be used in conjunction with the Analog Discovery Lab hardware board to accurately measure the V<​sub>​BE</​sub>​ vs. emitter current of an NPN transistor. Emitter current is used in this measurement rather than collector current but I<​sub>​E</​sub>​ and I<​sub>​C</​sub>​ are essentially the same given a high beta transistor. The op-amp supplies the base current and any bias current that might flow in the 2+ scope input while forcing the emitter of the transistor to the (virtual) ground potential. Negative voltages applied by waveform generator W1 set the emitter current through the 1KΩ resistor. The same circuit can be used to measure PNP transistors by connecting the collector to Vn rather than Vp. Positive voltages applied by generator W1 set the emitter current through the 1KΩresistor.+The circuit below, figure ​14, can be used in conjunction with the ADALM2000 ​to accurately measure the V<​sub>​BE</​sub>​ vs. emitter current of an NPN transistor. Emitter current is used in this measurement rather than collector current but I<​sub>​E</​sub>​ and I<​sub>​C</​sub>​ are essentially the same given a high beta transistor. The op-amp supplies the base current and any bias current that might flow in the 2+ scope input while forcing the emitter of the transistor to the (virtual) ground potential. Negative voltages applied by waveform generator W1 set the emitter current through the 1KΩ resistor. The same circuit can be used to measure PNP transistors by connecting the collector to Vn rather than Vp. Positive voltages applied by generator W1 set the emitter current through the 1KΩresistor.
  
-{{ :​university:​courses:​electronics:​a4_f10.png?500 |}}+{{ :​university:​courses:​electronics:​a4_f10_1.png?500 |}}
  
-<WRAP centeralign>​ Figure ​10 Circuit to measure V<​sub>​BE</​sub>​ </​WRAP>​+<WRAP centeralign>​ Figure ​14, Circuit to measure V<​sub>​BE</​sub>​ </​WRAP>​
  
 ===== Hardware Setup: ===== ===== Hardware Setup: =====
 +\\
 +{{ :​university:​courses:​electronics:​a4_nf10.png?​|}}
  
-The generator output W1 should be configured for a 100 Hz triangle wave with 2 volt amplitude and 2 volt offset (for an NPN device). The single ended input of scope channel 2+ is used to measure the voltage at the base of the transistor (optionally connect 2- to the emitter to remove any input offset of the op-amp). The setup should be configured with channel 1 connected to display the output of W1 and channel 2 connected to display the base voltage. The emitter current is calculated as the voltage of W1 / 1KΩ.+<WRAP centeralign>​ Figure 15, Circuit to measure V<​sub>​BE</​sub>​ breadboard connection </​WRAP>​ 
 + 
 +The generator output W1 should be configured for a 100 Hz triangle wave with 2 volt amplitude ​peak-to-peak ​and -2 volt offset (for an NPN device). The single ended input of scope channel 2+ is used to measure the voltage at the base of the transistor (optionally connect 2- to the emitter to remove any input offset of the op-amp). The setup should be configured with channel 1 connected to display the output of W1 and channel 2 connected to display the base voltage. The emitter current is calculated as the voltage of W1 / 1KΩ.
  
 ===== Procedure: ===== ===== Procedure: =====
 +
 {{ :​university:​courses:​electronics:​a4_e1.png?​300 |}} {{ :​university:​courses:​electronics:​a4_e1.png?​300 |}}
  
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 V<​sub>​T</​sub>​ is the Thermal Voltage\\ I<​sub>​C</​sub>​ is the collector current\\ V<​sub>​BE</​sub>​ is the base-emitter voltage\\ ∆V<​sub>​BE</​sub>​ is the base-emitter offset voltage\\ k is Boltzmann'​s constant\\ q is the electron charge\\ T is the absolute temperature\\ ln is the natural log\\ I<​sub>​S</​sub>​ is the collector-emitter saturation current V<​sub>​T</​sub>​ is the Thermal Voltage\\ I<​sub>​C</​sub>​ is the collector current\\ V<​sub>​BE</​sub>​ is the base-emitter voltage\\ ∆V<​sub>​BE</​sub>​ is the base-emitter offset voltage\\ k is Boltzmann'​s constant\\ q is the electron charge\\ T is the absolute temperature\\ ln is the natural log\\ I<​sub>​S</​sub>​ is the collector-emitter saturation current
  
-When the collector-emitter saturation currents (emitter area) are equal, they cancel each other out, and Equation 4 reduces to Equation 5+When the collector-emitter saturation currents (emitter area) are equal, they cancel each other out, and Equation 4 reduces to Equation 5.\\  
 + 
 +{{ :​university:​courses:​electronics:​a4_nf16.png?​500 |}} 
 + 
 +<WRAP centeralign>​ Figure 16, I<​sub>​E</​sub>​ vs V<​sub>​BE</​sub>​ Scopy Plot </​WRAP>​
  
 The I<​sub>​E</​sub>​ vs. V<​sub>​BE</​sub>​ data for two different size transistors is plotted in the next two graphs. The I<​sub>​E</​sub>​ vs. V<​sub>​BE</​sub>​ data for two different size transistors is plotted in the next two graphs.
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 {{ :​university:​courses:​electronics:​a4_f11.png?​500 |}} {{ :​university:​courses:​electronics:​a4_f11.png?​500 |}}
  
-<WRAP centeralign>​ Figure ​11 I<​sub>​E</​sub>​ vs. V<​sub>​BE</​sub>​ </​WRAP>​+<WRAP centeralign>​ Figure ​17, I<​sub>​E</​sub>​ vs. V<​sub>​BE</​sub>​ </​WRAP>​
  
 {{ :​university:​courses:​electronics:​a4_f12.png?​500 |}} {{ :​university:​courses:​electronics:​a4_f12.png?​500 |}}
  
-<WRAP centeralign>​ Figure ​12 I<​sub>​E</​sub>​ vs. V<​sub>​BE</​sub>​ </​WRAP>​+<WRAP centeralign>​ Figure ​18, I<​sub>​E</​sub>​ vs. V<​sub>​BE</​sub>​ </​WRAP>​
  
 The difference between these two curves, or delta V<​sub>​BE</​sub>,​ is plotted here. It can be seen that this difference is relatively constant over a wide range of current and is about 66 mV. From our V<​sub>​BE</​sub>​ equations this calculates to an effective emitter area difference of 12.7 between the two devices. The difference between these two curves, or delta V<​sub>​BE</​sub>,​ is plotted here. It can be seen that this difference is relatively constant over a wide range of current and is about 66 mV. From our V<​sub>​BE</​sub>​ equations this calculates to an effective emitter area difference of 12.7 between the two devices.
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 {{ :​university:​courses:​electronics:​a4_f13.png?​500 |}} {{ :​university:​courses:​electronics:​a4_f13.png?​500 |}}
  
-<WRAP centeralign>​ Figure ​13 DV<​sub>​BE</​sub>​ 2S1815 / 2D438 </​WRAP>​+<WRAP centeralign>​ Figure ​19, DV<​sub>​BE</​sub>​ 2S1815 / 2D438 </​WRAP>​
  
 ===== Questions: ===== ===== Questions: =====
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 ====== Alternative Method ====== ====== Alternative Method ======
  
-The circuits used earlier to make these measurements use the differential nature of the scope input channels of the Analog Discovery ​hardware. This was done, in part, to facilitate the conversion of the AWG’s voltage output into a current suitable to drive the transistor’s base. You may not always have access to instruments with differential input capability, such as standard bench top Oscilloscopes or the Analog Explorer student lab system. The following configuration,​ shown in figure 10, allows both the collector emitter voltage V<​sub>​CE</​sub>​ and the collector current I<​sub>​C</​sub>​ to be measured with ground referenced, singled ended, scope inputs while still converting the AWG voltage output into a suitable base current.+The circuits used earlier to make these measurements use the differential nature of the scope input channels of the ADALM2000 ​hardware. This was done, in part, to facilitate the conversion of the AWG’s voltage output into a current suitable to drive the transistor’s base. You may not always have access to instruments with differential input capability, such as standard bench top Oscilloscopes or the Analog Explorer student lab system. The following configuration,​ shown in figure 10, allows both the collector emitter voltage V<​sub>​CE</​sub>​ and the collector current I<​sub>​C</​sub>​ to be measured with ground referenced, singled ended, scope inputs while still converting the AWG voltage output into a suitable base current.
  
 {{ :​university:​courses:​electronics:​a4_f14.png?​500 |}} {{ :​university:​courses:​electronics:​a4_f14.png?​500 |}}
  
-<WRAP centeralign>​ Figure ​14 Alternate curve tracer circuit </​WRAP>​+<WRAP centeralign>​ Figure ​20, Alternate curve tracer circuit </​WRAP>​
  
 The circuit is built from one dual op-amp (ADTL082 for example or two single amplifiers) and a handful of resistors. Amplifier A1 is configured as a current to voltage converter such that the collector of the device under test (DUT) is forced to (virtual) ground and the voltage seen at its output represents I<​sub>​C</​sub>​ = V<​sub>​Scope2</​sub>/​100. The second amplifier, A2, is configured as what is known as the “improved” Howland current source. The staircase voltage from AWG2 is converted into a current and applied to the base of the DUT. The emitter of the DUT, and thus the V<​sub>​CE</​sub>​ is swept by the voltage of AWG1. The Howland current source will supply a fixed current independent of the emitter (and base) voltage. Since the collector of the DUT is at ground, the voltage ramp supplied by AWG1 must be negative, i.e. from -5V (or whatever the maximum negative voltage from the source is) to 0V. This is the minor concession that must be made to accommodate the single ended signal measurements. The V<​sub>​CE</​sub>​ as measured by Scope1 will need to be inverted to display a positive V<​sub>​CE</​sub>​ on the horizontal axis. The circuit is built from one dual op-amp (ADTL082 for example or two single amplifiers) and a handful of resistors. Amplifier A1 is configured as a current to voltage converter such that the collector of the device under test (DUT) is forced to (virtual) ground and the voltage seen at its output represents I<​sub>​C</​sub>​ = V<​sub>​Scope2</​sub>/​100. The second amplifier, A2, is configured as what is known as the “improved” Howland current source. The staircase voltage from AWG2 is converted into a current and applied to the base of the DUT. The emitter of the DUT, and thus the V<​sub>​CE</​sub>​ is swept by the voltage of AWG1. The Howland current source will supply a fixed current independent of the emitter (and base) voltage. Since the collector of the DUT is at ground, the voltage ramp supplied by AWG1 must be negative, i.e. from -5V (or whatever the maximum negative voltage from the source is) to 0V. This is the minor concession that must be made to accommodate the single ended signal measurements. The V<​sub>​CE</​sub>​ as measured by Scope1 will need to be inverted to display a positive V<​sub>​CE</​sub>​ on the horizontal axis.
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 This same circuit can be used to measure PNP devices by simply configuring the ramp signal to be positive, i.e. from 0V to the maximum positive swing of the source. This same circuit can be used to measure PNP devices by simply configuring the ramp signal to be positive, i.e. from 0V to the maximum positive swing of the source.
  
 +<WRAP round download>​
 +** Lab Resources:​**
 +  * Fritzing files: [[downgit>​education_tools/​tree/​master/​m2k/​fritzing/​bjt_curve_bb | bjt_curve_bb]]
 +  * LTSpice files: [[downgit>​education_tools/​tree/​master/​m2k/​ltspice/​bjt_curve_ltspice | bjt_curve_ltspice]]
 +  * Stairstep signal: [[downgit>​education_tools/​blob/​master/​m2k/​import_waveforms/​waveforms_sg/​stairstep.csv | stairstep]]
 +</​WRAP>​
 ==== For further reading on the Howland current source: ==== ==== For further reading on the Howland current source: ====
  
-[[http://​www.cirrus.com/​en/​pubs/​whitePaper/​199210-Apex-Versatile_current_source_circuits.pdf|http://​www.cirrus.com/​en/​pubs/​whitePaper/​199210-Apex-Versatile_current_source_circuits.pdf]] +[[adi>static/​imported-files/​application_notes/​236037846AN_843.pdf|http://​www.analog.com/​static/​imported-files/​application_notes/​236037846AN_843.pdf]]
- +
-[[http://​www.analog.com/​static/​imported-files/​application_notes/​236037846AN_843.pdf|http://​www.analog.com/​static/​imported-files/​application_notes/​236037846AN_843.pdf]]+
  
 [[http://​michaelgellis.tripod.com/​howland.html|http://​michaelgellis.tripod.com/​howland.html]] [[http://​michaelgellis.tripod.com/​howland.html|http://​michaelgellis.tripod.com/​howland.html]]
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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]]**
  
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university/courses/electronics/electronics-lab-4.txt · Last modified: 26 Jan 2021 15:32 by Doug Mercer