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university:courses:electronics:electronics-lab-12 [23 Mar 2017 16:20] – [Materials:] Doug Mercer | university:courses:electronics:electronics-lab-12 [25 Jun 2020 22:07] (current) – external edit 127.0.0.1 | ||
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- | ====== Activity | + | ====== Activity: BJT Differential pair ====== |
===== Objective: ===== | ===== Objective: ===== | ||
To investigate the simple differential amplifier using NPN transistors. | To investigate the simple differential amplifier using NPN transistors. | ||
- | First a few notes on hardware limitation issues. The waveform generator in the Analog Discovery Lab system has a high output bandwidth and with that high bandwidth comes wide band noise. The input signal level needed for the measurements in this lab activity is rather small because of the gain of the differential amplifier. If the waveform generator output were used directly the signal to noise ratio of its output is not high enough. The signal to noise ratio can be improved by increasing the signal level and then placing an attenuator and filter ( figure 1 ) between the generator outputs and the circuit inputs. The materials needed for this are: | + | First a few notes on hardware limitation issues. The waveform generator in the ADALM2000 |
2 - 100Ω resistors\\ | 2 - 100Ω resistors\\ | ||
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===== Hardware Setup: ===== | ===== Hardware Setup: ===== | ||
- | The first waveform generator should be configured for a 200 Hz Triangle wave with 2 volts amplitude and 0 offset. The second generator should be configured also for a 200 Hz Triangle wave with 2 volts amplitude and 0 volts offset but with 180 degree phase. The resistor dividers will reduce the signal amplitude seen at the bases of Q< | + | {{: |
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+ | <WRAP centeralign> | ||
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+ | The first waveform generator should be configured for a 200 Hz Triangle wave with 4 volts amplitude | ||
===== Procedure: ===== | ===== Procedure: ===== | ||
The following data should be taken: the X axis is the output of the arbitrary waveform generator and the Y axis is scope channel 2 using both the 2+ and 2- inputs. By changing the value of R< | The following data should be taken: the X axis is the output of the arbitrary waveform generator and the Y axis is scope channel 2 using both the 2+ and 2- inputs. By changing the value of R< | ||
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+ | <WRAP centeralign> | ||
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+ | <WRAP centeralign> | ||
====== Using a current source as the tail current.====== | ====== Using a current source as the tail current.====== | ||
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{{ : | {{ : | ||
- | <WRAP centeralign> | + | <WRAP centeralign> |
- | ====== Measuring Common Mode gain ====== | + | ===== Hardware Setup: |
- | Common mode rejection is a key aspect of the differential amplifier. CMR can be measured by connecting the base of both transistors Q<sub>1</sub> and Q<sub>2</sub> to the same input source. The plot below shows the differential output for both the resistively biased and current source | + | {{: |
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+ | <WRAP centeralign> Figure 6 Differential pair with tail current source Breadboard Circuit | ||
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+ | ===== Procedure: ===== | ||
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+ | Same procedure as for the tail resistor. | ||
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+ | <WRAP centeralign>{{: | ||
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+ | <WRAP centeralign> | ||
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+ | ====== Measuring Common Mode gain ====== | ||
{{ : | {{ : | ||
- | <WRAP centeralign> | + | <WRAP centeralign> |
+ | |||
+ | Common mode rejection is a key aspect of the differential amplifier. CMR can be measured by connecting the base of both transistors Q< | ||
+ | |||
+ | ===== Hardware Setup: ===== | ||
+ | |||
+ | {{: | ||
+ | |||
+ | <WRAP centeralign> | ||
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+ | ===== Procedure: ===== | ||
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+ | {{: | ||
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+ | <WRAP centeralign> | ||
===== Questions: ===== | ===== Questions: ===== | ||
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Repeat the common mode gain measurements on the circuit shown in figure 3 with the tail current source. How has the result changed and why. | Repeat the common mode gain measurements on the circuit shown in figure 3 with the tail current source. How has the result changed and why. | ||
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+ | <WRAP round download> | ||
+ | **Resources: | ||
+ | * Fritzing files: [[downgit> | ||
+ | * LTspice files: [[downgit> | ||
+ | </ | ||
**Return to Lab Activity [[university: | **Return to Lab Activity [[university: | ||