模电ch11
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+VCC
0
vo1
Rc iC1
0
+ vo vo1 T1 vo2 T2
Rc iC2
VC1
0
vi1 0
Rb vi1
iE1
+ -
iE1 iE Re
iE2
Rb
vi2 0
+ iE1
vi2
-VEE
IE1
iE = 2iE1 = 2iE2
IE1
In addition：
0
Re?
2Re
0
2. Rejecting Common-Mode signals
11.0 Preview
1. Direct-Coupled Amplifier # Why the integrated opamp is direct-coupled？ •It is almost impossible to fabricate capacitors on an IC, C is in microfarad range.
vic
From equations of vid、 vic we get
vid vid vi1 = vic , vi2 = vic 2 2
K CMR =
Common input AVD
Diffamp
Common-mode rejection ratio
AVC
vid = vi1 vi2
1 vic = (vi1 vi2 ) 2 vid vi1 = vic 2 vid vi2 = vic 2
vo
Only difference inputs are applied
0
+VCC
vo2
vo1
Rc iC1 vo1 T1
+ vo vo2 T2
Rc iC2
VC1
VC2
0
Rb vi1
iE1
vi1 0
+ -
iE1 iE Re
iE2
Rb
0
+ iE2
vi2
vi2 0
-VEE
IE1
In addition:
0
iE = 0 vRe = 0
• An amplifier can be used to amplify dc signal.
2. Disadvantage of direct-coupled amplifier Offset voltage: op-amp produces an output offset voltage without any external input signal.
V Drift 1 V+ 10 mV
The methods to reduce offset voltage: Using nonlinear components to compensate. Using differential circuit.
4. Terminology and Qualitative Description(P136)
11.1 Basic BJT Difference Pair (P137)
1. Structure and Operating (1) DC analysis • T1 and T1 are matched or identical. RC1 = RC2. vi1= vi2 =0
I C1 = I C2 1 IC I0 2
vid = vi1 vi2 Diff-mode input + 1 vic = (vi1 vi2 )com-mode input 2 vi1
+ + vid vid -
vo AVD = vid vo AVC = vic
Diff-mode output
Diff-mode gain
+
+ vi2 -
Two input Two output
11.1 Basic BJT Difference Pair
applied common-mode voltage
applied differential-mode voltage
Working methods
Output
Inpu t
two-sided input, two-sided output
Re? Short
IE2
0
1. Structure and Operating
(2) AC analysis
• Only difference inputs are applied, vi1= vi2 , causing vc1=
vc2 , thus, vo= vc1 vc2 0. The input signal is amplified.
1V 4 110 V/℃ 1000 10
11.0 Preview Example Assume AV 1 = 100,
AV 2 = 100, AV 3 = 1 。
Drift 1 V+ 10 mV Drift 10 mV+100 V
Hale Waihona Puke If the thermal drift of the
Huazhong University of Science and Technology The Department of Electronics and Information Engineering
First Term 09/10
Electronic Circuit Analysis and Design
DiffDiffamp amp (a)
+ vo -
+
+ vo2 -
vo1
-
Com-mode output
Com-mode gain
Diffvid amp Difference amplifier block diagram (b)
Differential input
Output voltage
vo = vo vo AVDv+ AVCvic id
11.0 Preview 2. Disadvantage of direct-coupled amplifier Main reasons:
Power supply voltage changing, causing dc biasing current to change, output voltage will also change. The parameters of transistors change with temperature. Thermal drift is main reason.
The com-mode signal has the same amplitude and the same phase. The diff-mode signal has the same amplitude but the opposite phase.
For example:
vi1 10sin t
3. Thermal voltage drift: is defined as the rate of change of input offset voltage per unit change in temperature.
For example:
T
10℃
Drift 1V
Thermal voltage drift=?
Ch11 Differential and Multistage Amplifiers
11.0 Preview 11.1 Basic BJT Difference Pair
11.2 FET Difference Amplifier
11.3 DC Transfer Characteristic
Ch11 Differential and Multistage Amplifiers
11.1 Basic BJT Difference Pair
11.1 Basic BJT Difference Pair
Circuit structure:
T1,T2 is Completely
symmetrical Use of positive and negative power supply
Working methods
Output
Input
two-sided input, one-sided output
Working methods
Output
input
one-sided input, two-sided output
Working methods Output
input
one-sided input, one-sided output
VCE1 = VCE2
VCC I C RC VE
Basic differential circuit
VCC I C Rc (0.7V) IC I B1 I B2 β
1. Structure and Operating
(2) AC analysis
vid vi1 = 2 v vi2 = id 2
Common-Mode signals • Noise, thermal drift or other unwanted signals will be present in both terminals. They are the common-mode signals. • A differential amp is expected to reject the common voltages.
Dr. Tianping Deng Email: dengtp@
Contents
PART 1 SEMICONDUCTOR DEVICES AND BASIC APPLICATIONS Chapter 1 Semiconductor Materials and Diodes Chapter 2 Diode Circuits Chapter 3 The Field-Effect Transistor Chapter 4 Basic FET Amplifiers Chapter 5 The Bipolar Junction Transistor Chapter 6 Basic BJT Amplifiers Chapter 7 Frequency Response Chapter 8 Output Stages and Power Amplifiers PART 2 ANALOG ELECTRONICS Chapter 9 Ideal Operational Amplifiers and Op-Amp Circuits Chapter 10 Integrated Circuit Biasing and Active Loads Chapter 11 Differential and Multistage Amplifiers Chapter 12 Feedback and Stability Chapter 13 Operational Amplifier Circuits Chapter 14 Nonideal Effects in Operational Amplifier Circuits Chapter 15 Applications and Design of Integrated Circuits
vid vi1 = vic 2
vi 2 4sin t
vid vi2 = vic 2
vid 6sin t vic 7sin t
com-mode input
Diff-mode input
11.1 Basic BJT Difference Pair (P136) 1. Structure and Operating 2. Rejecting Common-Mode signals 3. Calculating 4. Comparing Properties of Diff-Amp Example
vo
0
vo1
vo2
VC1
VC2
0
Basic difference amplifier
0
1. Structure and Operating
(2) AC analysis
vo
v i1 = v ic
v i2 = v ic
vo1 VC1
Only Common-Mode signals inputs are applied
first stage is 100 V，causing the output drift is 1V. Drift 100 If the thermal drift of the second stage is 100 V ， causing the output drift is 10mV.
0
vo1
Rc iC1
0
+ vo vo1 T1 vo2 T2
Rc iC2
VC1
0
vi1 0
Rb vi1
iE1
+ -
iE1 iE Re
iE2
Rb
vi2 0
+ iE1
vi2
-VEE
IE1
iE = 2iE1 = 2iE2
IE1
In addition：
0
Re?
2Re
0
2. Rejecting Common-Mode signals
11.0 Preview
1. Direct-Coupled Amplifier # Why the integrated opamp is direct-coupled？ •It is almost impossible to fabricate capacitors on an IC, C is in microfarad range.
vic
From equations of vid、 vic we get
vid vid vi1 = vic , vi2 = vic 2 2
K CMR =
Common input AVD
Diffamp
Common-mode rejection ratio
AVC
vid = vi1 vi2
1 vic = (vi1 vi2 ) 2 vid vi1 = vic 2 vid vi2 = vic 2
vo
Only difference inputs are applied
0
+VCC
vo2
vo1
Rc iC1 vo1 T1
+ vo vo2 T2
Rc iC2
VC1
VC2
0
Rb vi1
iE1
vi1 0
+ -
iE1 iE Re
iE2
Rb
0
+ iE2
vi2
vi2 0
-VEE
IE1
In addition:
0
iE = 0 vRe = 0
• An amplifier can be used to amplify dc signal.
2. Disadvantage of direct-coupled amplifier Offset voltage: op-amp produces an output offset voltage without any external input signal.
V Drift 1 V+ 10 mV
The methods to reduce offset voltage: Using nonlinear components to compensate. Using differential circuit.
4. Terminology and Qualitative Description(P136)
11.1 Basic BJT Difference Pair (P137)
1. Structure and Operating (1) DC analysis • T1 and T1 are matched or identical. RC1 = RC2. vi1= vi2 =0
I C1 = I C2 1 IC I0 2
vid = vi1 vi2 Diff-mode input + 1 vic = (vi1 vi2 )com-mode input 2 vi1
+ + vid vid -
vo AVD = vid vo AVC = vic
Diff-mode output
Diff-mode gain
+
+ vi2 -
Two input Two output
11.1 Basic BJT Difference Pair
applied common-mode voltage
applied differential-mode voltage
Working methods
Output
Inpu t
two-sided input, two-sided output
Re? Short
IE2
0
1. Structure and Operating
(2) AC analysis
• Only difference inputs are applied, vi1= vi2 , causing vc1=
vc2 , thus, vo= vc1 vc2 0. The input signal is amplified.
1V 4 110 V/℃ 1000 10
11.0 Preview Example Assume AV 1 = 100,
AV 2 = 100, AV 3 = 1 。
Drift 1 V+ 10 mV Drift 10 mV+100 V
Hale Waihona Puke If the thermal drift of the
Huazhong University of Science and Technology The Department of Electronics and Information Engineering
First Term 09/10
Electronic Circuit Analysis and Design
DiffDiffamp amp (a)
+ vo -
+
+ vo2 -
vo1
-
Com-mode output
Com-mode gain
Diffvid amp Difference amplifier block diagram (b)
Differential input
Output voltage
vo = vo vo AVDv+ AVCvic id
11.0 Preview 2. Disadvantage of direct-coupled amplifier Main reasons:
Power supply voltage changing, causing dc biasing current to change, output voltage will also change. The parameters of transistors change with temperature. Thermal drift is main reason.
The com-mode signal has the same amplitude and the same phase. The diff-mode signal has the same amplitude but the opposite phase.
For example:
vi1 10sin t
3. Thermal voltage drift: is defined as the rate of change of input offset voltage per unit change in temperature.
For example:
T
10℃
Drift 1V
Thermal voltage drift=?
Ch11 Differential and Multistage Amplifiers
11.0 Preview 11.1 Basic BJT Difference Pair
11.2 FET Difference Amplifier
11.3 DC Transfer Characteristic
Ch11 Differential and Multistage Amplifiers
11.1 Basic BJT Difference Pair
11.1 Basic BJT Difference Pair
Circuit structure:
T1,T2 is Completely
symmetrical Use of positive and negative power supply
Working methods
Output
Input
two-sided input, one-sided output
Working methods
Output
input
one-sided input, two-sided output
Working methods Output
input
one-sided input, one-sided output
VCE1 = VCE2
VCC I C RC VE
Basic differential circuit
VCC I C Rc (0.7V) IC I B1 I B2 β
1. Structure and Operating
(2) AC analysis
vid vi1 = 2 v vi2 = id 2
Common-Mode signals • Noise, thermal drift or other unwanted signals will be present in both terminals. They are the common-mode signals. • A differential amp is expected to reject the common voltages.
Dr. Tianping Deng Email: dengtp@
Contents
PART 1 SEMICONDUCTOR DEVICES AND BASIC APPLICATIONS Chapter 1 Semiconductor Materials and Diodes Chapter 2 Diode Circuits Chapter 3 The Field-Effect Transistor Chapter 4 Basic FET Amplifiers Chapter 5 The Bipolar Junction Transistor Chapter 6 Basic BJT Amplifiers Chapter 7 Frequency Response Chapter 8 Output Stages and Power Amplifiers PART 2 ANALOG ELECTRONICS Chapter 9 Ideal Operational Amplifiers and Op-Amp Circuits Chapter 10 Integrated Circuit Biasing and Active Loads Chapter 11 Differential and Multistage Amplifiers Chapter 12 Feedback and Stability Chapter 13 Operational Amplifier Circuits Chapter 14 Nonideal Effects in Operational Amplifier Circuits Chapter 15 Applications and Design of Integrated Circuits
vid vi1 = vic 2
vi 2 4sin t
vid vi2 = vic 2
vid 6sin t vic 7sin t
com-mode input
Diff-mode input
11.1 Basic BJT Difference Pair (P136) 1. Structure and Operating 2. Rejecting Common-Mode signals 3. Calculating 4. Comparing Properties of Diff-Amp Example
vo
0
vo1
vo2
VC1
VC2
0
Basic difference amplifier
0
1. Structure and Operating
(2) AC analysis
vo
v i1 = v ic
v i2 = v ic
vo1 VC1
Only Common-Mode signals inputs are applied
first stage is 100 V，causing the output drift is 1V. Drift 100 If the thermal drift of the second stage is 100 V ， causing the output drift is 10mV.