Wiki

Differences

This shows you the differences between two versions of the page.

Link to this comparison view

Next revision
Previous revision
university:courses:electronics:electronics-lab-6 [27 Oct 2012 18:48]
Doug Mercer created
university:courses:electronics:electronics-lab-6 [25 Jun 2020 22:07] (current)
Line 1: Line 1:
-====== Activity ​6. BJT Current Mirror ======+====== ActivityBJT Current Mirror ======
  
 ===== Objective: ===== ===== Objective: =====
Line 7: Line 7:
 ===== Materials: ===== ===== Materials: =====
  
-Analog Discovery Lab hardware\\+ADALM2000 Active Learning Module\\
 Solder-less breadboard\\ Solder-less breadboard\\
 Jumper wires\\ Jumper wires\\
Line 22: Line 22:
  
 <WRAP centeralign>​ Figure 1 Current mirror test circuit </​WRAP>​ <WRAP centeralign>​ Figure 1 Current mirror test circuit </​WRAP>​
 +
 +{{ :​university:​courses:​electronics:​a6n_f2.png?​ |}}
 +
 +<WRAP centeralign>​ Figure 2 Breadboard Connection of Current mirror test circuit </​WRAP>​
 +
  
 ===== Hardware Setup: ===== ===== Hardware Setup: =====
  
-In the current mirror configuration,​ the opamp serves as a virtual ground at the mirror input (base) node to convert the voltage steps from AWG 2 ( W2 output ) into current steps through the 1KΩ resistor. The collector voltage is swept using a ramp from AWG 1(output W1) set to 3V peak to peak with the offset to 1.5V. V<​sub>​CE</​sub>​ of output device Q<​sub>​2</​sub>​ is measured differentially by scope inputs 1+, 1-. The mirror output current is measured by scope inputs 2+. 2- across 1KΩ resistor, R<​sub>​2</​sub>​.+In the current mirror configuration,​ the op amp serves as a virtual ground at the mirror input (base) node to convert the voltage steps from AWG 2 ( W2 output ) into current steps through the 1KΩ resistor. The collector voltage is swept using a ramp from AWG 1(output W1). Load the stairstep.csv file, set amplitude ​to 3V peak-to-peak with the offset to 1.5V.  
 +V<​sub>​CE</​sub>​ of output device Q<​sub>​2</​sub>​ is measured differentially by scope inputs 1+, 1-. The mirror output current is measured by scope inputs 2+. 2- across 1KΩ resistor, R<​sub>​2</​sub>​.
 If you don't want to use the op-amp configuration the following simplified configuration can be used as well. If you don't want to use the op-amp configuration the following simplified configuration can be used as well.
  
 {{ :​university:​courses:​electronics:​a6_f2.png?​500 |}} {{ :​university:​courses:​electronics:​a6_f2.png?​500 |}}
  
-<WRAP centeralign>​ Figure ​Alt, Simple current mirror test circuit </​WRAP>​+<WRAP centeralign>​ Figure ​Alt, Simple current mirror test circuit </​WRAP>​ 
 + 
 +{{ :​university:​courses:​electronics:​a6n_f4.png?​ |}} 
 + 
 +<WRAP centeralign>​ Figure 4 Breadboard Connection of Simple current mirror test circuit </​WRAP>​
  
 ===== Procedure: ===== ===== Procedure: =====
Line 43: Line 53:
   ​   ​
 Identical transistors by definition have the same I<​sub>​S</​sub>​. In the simple current mirror, both transistors have the same V<​sub>​BE</​sub>​. Thus, both transistors will have the same I<​sub>​C</​sub>​ and if base currents are ignored, Iin = Iout. Actually I<​sub>​C1</​sub>​is I<​sub>​in</​sub>​ - (I<​sub>​B1</​sub>​ + I<​sub>​B2</​sub>​). Identical transistors by definition have the same I<​sub>​S</​sub>​. In the simple current mirror, both transistors have the same V<​sub>​BE</​sub>​. Thus, both transistors will have the same I<​sub>​C</​sub>​ and if base currents are ignored, Iin = Iout. Actually I<​sub>​C1</​sub>​is I<​sub>​in</​sub>​ - (I<​sub>​B1</​sub>​ + I<​sub>​B2</​sub>​).
 +
 +Plot the two waveforms using the Oscilloscope provided by the Scopy tool.
 +{{ :​university:​courses:​electronics:​a6n_f5.png?​500 |}}
 +
 +<WRAP centeralign>​ Figure 5 Current Mirror waveforms, W2 at 10kHz Sample Rate</​WRAP>​
 +
  
 ===== Questions: ===== ===== Questions: =====
Line 50: Line 66:
 ====== Current Mirror with Base Current Compensation ====== ====== Current Mirror with Base Current Compensation ======
  
-Modify the simple mirror circuit by adding the base current compensation transistor Q<​sub>​3</​sub>​ as shown below in figure ​3Repeat the same procedure you followed for the simple mirror circuit.  +Modify the simple mirror circuit by adding the base current compensation transistor Q<​sub>​3</​sub>​ as shown below in figure ​6
 {{ :​university:​courses:​electronics:​a6_f3.png?​500 |}} {{ :​university:​courses:​electronics:​a6_f3.png?​500 |}}
  
-<WRAP centeralign>​ Figure ​Current Mirror with Base Current Compensation </​WRAP>​+<WRAP centeralign>​ Figure ​Current Mirror with Base Current Compensation ​</​WRAP>​ 
 + 
 +=====Hardware Setup===== 
 +{{ :​university:​courses:​electronics:​a6n_f7.png?​ |}} 
 + 
 +<WRAP centeralign>​ Figure 7 Breadboard Connection of Current Mirror with Base Current Compensation </​WRAP>​ 
 +=====Procedure ===== 
 +Repeat the same procedure you followed for the simple mirror circuit.  
 +{{ :​university:​courses:​electronics:​a6n_f8.png?​500 |}} 
 + 
 +<WRAP centeralign>​ Figure 8 Current Mirror waveforms, W2 at 10kHz Sample Rate </​WRAP>​
  
 ===== Questions: ===== ===== Questions: =====
Line 64: Line 89:
 ===== References, further reading: ===== ===== References, further reading: =====
  
-[http://​en.wikipedia.org/​wiki/​Current_mirror-http://​en.wikipedia.org/​wiki/​Current_mirror]+http://​en.wikipedia.org/​wiki/​Current_mirror
  
 ====== Wilson Current Mirror ====== ====== Wilson Current Mirror ======
  
-Modify the simple mirror into a Wilson Mirror as shown below in figure ​4. Repeat the same procedure you followed for the simple mirror circuit. ​+Modify the simple mirror into a Wilson Mirror as shown below in figure ​9. Repeat the same procedure you followed for the simple mirror circuit. ​
  
 {{ :​university:​courses:​electronics:​a6_f4.png?​500 |}} {{ :​university:​courses:​electronics:​a6_f4.png?​500 |}}
  
-<WRAP centeralign>​ Figure ​Wilson current mirror </​WRAP>​+<WRAP centeralign>​ Figure ​Wilson current mirror ​</​WRAP>​ 
 +=====Hardware Setup===== 
 +{{ :​university:​courses:​electronics:​a6n_f10.png?​ |}} 
 + 
 +<WRAP centeralign>​ Figure 10 Breadboard Connection of Wilson current mirror </​WRAP>​ 
 +=====Procedure ===== 
 +Repeat the same procedure you followed for the simple mirror circuit.  
 +{{ :​university:​courses:​electronics:​a6n_f11.png?​500 |}} 
 + 
 +<WRAP centeralign>​ Figure 11 Current Mirror waveforms, W2 at 10kHz Sample Rate </​WRAP>​
  
 ===== Questions: ===== ===== Questions: =====
Line 86: Line 120:
 ====== Widlar current mirror ====== ====== Widlar current mirror ======
  
-Modify the simple mirror into a Widlar Mirror as shown below in figure ​5. Repeat the same procedure you followed for the simple mirror circuit. In addition to the same quantities and graphs, does your data indicate any advantage to this circuit? Any disadvantages?​+Modify the simple mirror into a Widlar Mirror as shown below in figure ​12. Repeat the same procedure you followed for the simple mirror circuit. In addition to the same quantities and graphs, does your data indicate any advantage to this circuit? Any disadvantages?​
  
 {{ :​university:​courses:​electronics:​a6_f5.png?​500 |}} {{ :​university:​courses:​electronics:​a6_f5.png?​500 |}}
  
-<WRAP centeralign>​ Figure ​Widlar current mirror </​WRAP>​+<WRAP centeralign>​ Figure ​12 Widlar current mirror ​</​WRAP>​ 
 +=====Hardware Setup===== 
 +{{ :​university:​courses:​electronics:​a6n_f13.png?​ |}} 
 + 
 +<WRAP centeralign>​ Figure 13 Breadboard Connection of Widlar current mirror </​WRAP>​ 
 +=====Procedure ===== 
 +Repeat the same procedure you followed for the simple mirror circuit.  
 +{{ :​university:​courses:​electronics:​a6n_f14.png?​500 |}} 
 + 
 +<WRAP centeralign>​ Figure 14 Current Mirror waveforms, W2 at 10kHz Sample Rate </​WRAP>​
  
 ===== Questions: ===== ===== Questions: =====
Line 120: Line 163:
 ===== Directions: ===== ===== Directions: =====
  
-The diode configuration with nearly zero turn on voltage from activity 2 is used here, in figure ​6, to make a current mirror. The current input node at the collector of Q<​sub>​1</​sub>​ (base of PNP Q<​sub>​3</​sub>​) is now much closer to ground compared to the conventional current mirror. What advantages would this have over the conventional mirror?+The diode configuration with nearly zero turn on voltage from activity 2 is used here, in figure ​15, to make a current mirror. The current input node at the collector of Q<​sub>​1</​sub>​ (base of PNP Q<​sub>​3</​sub>​) is now much closer to ground compared to the conventional current mirror. What advantages would this have over the conventional mirror?
  
 {{ :​university:​courses:​electronics:​a6_f6.png?​500 |}} {{ :​university:​courses:​electronics:​a6_f6.png?​500 |}}
  
-<WRAP centeralign>​ Figure ​Low input head room mirror </​WRAP>​+<WRAP centeralign>​ Figure ​15 Low input head room mirror </​WRAP>​
  
-Ideally the collector of PNP Q<​sub>​3</​sub>​ would be connected to some negative voltage with respect to groundTry connecting the collector of Q<​sub>​3</​sub>​ to the negative board supply Vn. What happens? Can the input node of the mirror get even closer to ground now?+=====Hardware Setup===== 
 +{{ :​university:​courses:​electronics:​a6n_f16.png|}}
  
 +<WRAP centeralign>​ Figure 16 Breadboard Connection of Low input head room mirror </​WRAP>​
 +=====Procedure =====
 +Repeat the same procedure you followed for the simple mirror circuit. ​
 +{{ :​university:​courses:​electronics:​a6n_f17.png?​500 |}}
  
 +<WRAP centeralign>​ Figure 17 Current Mirror waveforms, W1 at 10kHz Sample Rate </​WRAP>​
 +
 +
 +Ideally the collector of PNP Q<​sub>​3</​sub>​ would be connected to some negative voltage with respect to ground. Try connecting the collector of Q<​sub>​3</​sub>​ to the negative board supply Vn. What happens? Can the input node of the mirror get even closer to ground now?
  
 +<WRAP round download>​
 +**Resources:​**
 +  * Fritzing files: [[downgit>​education_tools/​tree/​master/​m2k/​fritzing/​bjt_current_mirror_bb | bjt_current_mirror_bb]]
 +  * LTspice files: [[downgit>​education_tools/​tree/​master/​m2k/​ltspice/​bjt_current_mirror_ltspice | bjt_current_mirror_ltspice]]
 +</​WRAP>​
  
 +**Return to Lab Activity [[university:​courses:​electronics:​labs|Table of Contents]]**
university/courses/electronics/electronics-lab-6.1351356491.txt.gz · Last modified: 27 Oct 2012 18:48 by Doug Mercer