Differential Amplifiers

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Differential Amplifiers

• Prof. Paul Hasler

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Differential Transistor Pairs
MOSFET Diff-Pair
BJT Diff-Pair
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Differential Transistor Pairs
MOSFET Diff-Pair
BJT Diff-Pair
The bottom transistor (the one with Ibias) sets
the total current
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Differential Transistor Pairs
MOSFET Diff-Pair
BJT Diff-Pair
The bottom transistor (the one with Ibias) sets
the total current
The upper two transistors compete for a fraction
of this current
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Analysis of Diff-Pair
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Analysis of Diff-Pair
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Analysis of Diff-Pair
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Analysis of Diff-Pair
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Analysis of Diff-Pair
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Analysis of Diff-Pair
Source of Common-Mode Gain
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Analysis of Diff-Pair
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Analysis of Diff-Pair
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Differential Pair Currents
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Iout
Iout-
2.5
2
(nA)
1.5
Output current
1
0.5
0
-0.
4
-0.
3
-0.
2
-0.
1
0
0.1
0.2
0.3
0.4
Differential input
voltage (V)
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Transistor Leg Currents
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Transistor Leg Currents
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BJT Differential Pair Analysis

-
Iout
Iout
V1
V2
Vb
GND
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BJT Differential Amplifier

-
Iout
Iout
V1
V2
Vb
GND
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BJT Differential Amplifier
V1
V2
Vb
GND
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BJT Differential Amplifier
Fixed output voltage Current output
Zero output current Voltage output
V1
V2
Vb
GND
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Basic Differential Amplifier
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Transfer Functions
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Wide-Output Range Differential Amplifier
Simple differential amplifer
"Vmin" effect
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Wide-Output Range Differential Amplifier
Wide-output range amplifier
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Wide-Output Range Differential Amplifier
Wide-output range amplifier
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A Unity-Gain Follower
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A Unity-Gain Follower
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A Unity-Gain Follower
Amp Gain Av
Av
Solving Vout Vin
1 Av
A more ideal Follower / Buffer Circuit
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A Unity-Gain Follower
Amp Gain Av
Solving Vout Vin
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A Unity-Gain Follower
Amp Gain Av
Solving Vout Vin
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Differential Pairs / Amplifiers

• Differential Transistor Pairs
• Differential Amplifiers
• Unity-Gain Amplifiers