Download + V

electronics
electronics
• About some fundamental semiconductor
devices
• Diode 半導體二極管 , transistor晶體管 &
Op Amp 運算放大器
electronics
• Semiconductor materials:
– n-type (e-) & p-type (hole)
• Using semiconductor, we can control the
amount current flowing through the circuit.
• Logical and mathematical operation can be
carried out.
Semiconductor diode ( 半導體二極管 )
I
A
B
p n
• To allow current flow in one direction only
• A  B: current can pass (VA > VB) [Forward biased]
• B  A: no current can pass [Reversed biased]
Ideal diode
R
6V
=
0V
6V
R
0V
R
0V
=
6V
0V
R
6V
I – V characteristics 特性曲線
I
Ideal
Real
reverse
forward
Junction
potential
barrier
Why
V
Vf = 0.7V
Forward bias or forward voltage Vf ( 正向偏壓 )
Vf = 0.6V to 0.8V for silicon diodes
Rectification 整流
• a.c.  d.c.
half-wave rectification 半波整流
Vin
Vout
Reverse bias:
Vout = 0
Vout
Vf
Forward bias:
Vout = Vin – Vf
rectified
t
full-wave rectification 全波整流
• Centre-tapped full-wave rectifier ( 中插頭全波整流器 )
• Two diodes and one transformer are used
D1
A
main
C
Direction of current
I
B
load at output
D2
Va > Vb > Vc: A  D1  E  B
Vc > Vb > Va: C  D2  E  B
E
Bridge full-wave rectifier 橋式整流器
• Four diodes are used.
A
D4
D1
Y
X
D3
D2
B
I
load at
output
Va > Vb: A  D1  X  R  Y  D3  B
Vb > Va: B  D2  X  R  Y  D4  A
T/2 = 0.01S
• Bridge full-wave rectifier 橋式整流器
• Unidirectional but pulsating voltage
• If the original frequency is 50Hz, the peak
occurs at every 0.01s.
Smoothing ( 濾波 )
Storage capacitor (reservoir) ( 存儲電容器 )
Simple smoothing circuit ( 平流電路 )
rectified
+
unsmoothed d.c
已整流但未平流

直流電
+
C
charge up discharge
T/2
Without C
R
load at
output
with C
ripple 紋波

• Time constant  = RC
• Larger time constant  smoother output
• in order to have a good smoothing effect,
RC should be very large compared to T/2
(time between peaks occurs).
Filter capacitor ( 濾波電容器 )
 filter circuit ( 濾波電路 )
a.c.
rectified +
unsmoothed
d.c
已整流但未平
流直流電
L
+
C
+
R
C2
load at
output
d.c.
L and C2 in series, acts as a potential divider
L: read a.c. component
C: read d.c. component
a.c.
rectified +
unsmoothed
d.c
已整流但未平
流直流電
L
+
C
+
R
C2
load at
output
d.c.
XL = L high reactance for a.c. (high f)
low reactance for d.c. (f  0)
XC = 1/ C
low reactance for a.c. (high f)
high reactance for d.c. (f  0)
NPN transistor ( NPN 晶體管 )
Emitter
Collector
N-type
p-type
N-type
p-type
IC
IB
C
B
Base
VCE
E
VBE
IE
NPN transistor ( NPN 晶體管 )
• B: base基極 C: collector集電極 E: emitter 發射極
• IB: base current
• IC: collector current
• IE: emitter current
IC
IB
C
B
• Used as switches or amplifiers VBE
• In an integrated circuit (IC):
contains thousands of transistors
VCE
E
IE
http://micro.magnet.fsu.edu/electromag
/java/transistor/index.html
Making of a transistor
Investigation
RL
ICRL
IBRB
Vin
RB
VCC
VBE
VCE
Investigation
RL
ICRL
IBRB
Vin
RB
VCC
VBE
VCE
Investigation
RL
ICRL
IBRB
Vin
RB
VCC
VBE
VCE
Investigation
RL
IC
IB
Vin
RB
VCC
VBE
VCE
Common emitter configuration
IC
• E is earthed (0V)
IB
C
B
VCE
E
VBE
IE
Two important relationships
• IE = IB + I C
IC
• Current gain 電流增益
 = IC / I B
I
B
= IC / IB
• Typically,  > 100
•  is transistor dependent.
C
B
E
IE
Two important relationships
 = IC / IB
 IC = IB
IC
IB
IC / mA
C
B
E
Slope = 
IB / mA
IE
Max IC is limited by VCC and RL
RL
ICRL
IBRB
VCC
Max IC = VccRB/ RL
Vin
VBE
Vcc = IC RL+VCE
VCE
Max IC is limited by VCC and RL
IC / mA
saturated
Max IC = Vcc / RL
Slope = 
RL
IB / mA
ICRL
IBRB
Vin
RB
VCC
VBE
VCE
• Input ( base ) characteristic ( IBVBE curve )
( 輸入特徵曲線 )
•Same as a diode
IB
IB
ideal
VBE
VBE
0.7 V
• Input ( base ) characteristic ( IBVBE curve )
( 輸入特徵曲線 )
• Same as a diode
•ideally, VBE = 0.7V
I
Vin  0.7V, VBE = VIN, IB =0
B
ideal
Vin > 0.7V, VIN = IB RB + VBE
VBE
IBRB
VIN
VBE
0.7 V
Vin > 0.7V, VIN = IB RB + VBE
IB
IBRB
VIN
ideal
VBE
VIN
VBE
IN
0.7 V
Vin > 0.7V, VIN = IB RB + VBE
IBRB
VIN
IBIB
IB
ideal
ideal
VBE ideal
VBE
IN
VIN
VIN
0.7 V
0.7
V
0.7VV
in
Vin > 0.7V, VIN = IB RB + VBE
IBRB
VIN
VBE
VIN - VBE = IB RB
IB = VIN / RB - VBE / RB
IB
ideal
0.7 V
• IB = VIN /RB - VBE /RB
or IB = VIN /RB - 0.7 /RB
Vin
Function of RB: limiting the IB & IC
( IBVIN curves )
VIN
• IB = VIN /RB - 0.7 /RB
Output ( collector ) characteristic
( ICVCE curves ) ( 輸出特徵曲線 )
VCC
• VCE = VCC – IC RL
Ideally
IC
5.2 mA
IB = 40 mA
3.9 mA
IB = 30 mA
2.6 mA
IB = 20 mA
 IC
IB = 10 mA
1.3 mA
0.2 V
1V
VCE
IB = 0  IC = 0
VCE＞0.2 V, IC becomes constant
IC =  IB
Typically,  > 100
4mA
4mA
4mA
IB = 0.04mA
IB = 0.04mA
IB = 0.04mA
Current transfer characteristic
( IC  IB curve ) ( 電流傳輸特徵曲線 )
 = IC / IB= IC /  IB
IC / mA
Max IC = Vcc / RL
Slope = 
IB / mA
Input/output voltage characteristic
( 輸入/輸出電壓特徵曲線 )
Vout = VCE / V
cutoff
6.0
Vout = VCE
0.2
* ideal
linear region
0.5
0.7
saturation
Vin /V
http://www.ngsir.netfirms.com/englishhtm/Amplifier.htm
Vout = VCE / V
Cut-off region
cutoff
6.0
•
•
•
•
•
Vcc = 6 V
Vin＜0.7 V
0.2
Ib = 0  Ic = 0
By VCC = ICRL + Vout
 Vout = Vcc = 6 V
ideal
linear region
Slope = A
(voltage gain)
0.5
0.7
saturation
Vin /V
Linear region 線性區域，放大區
Vout
Slope  
  A   voltage gain ( 電壓增益)
Vin
• Vout varies linearly with Vin
• Input: Vin＞0.7 V
 IB＞0 and VBE = constant
• also
Vin = VBE + IBRB
d [ Vin = VBE + IBRB ]
 Vin = RB IB ….. (1)
• Output:
VCC = ICRL + Vout
d[ VCC = ICRL + Vout ]
0 = RLIC + Vout … (2)
( 2)  (1)

Vout
RL I C
A


Vin
RB I B
RL
A  
RB
A = slope at the linear region
Saturation ( 飽和 )
• Vout remains almost zero  0.1-0.2 V
• Since IC has a maximum value Vcc / RL when
saturated, given by
Vout  0
saturation occurs
when
Ib > (Ib)saturation = (Ic)max /
Vin> (Vin)saturated = IbRB  VBE
Transistor as a linear voltage amplifier
線性電壓放大器
IC
Vi
C
Signal
generator
vi
RL
IB
IB
Vin
Vo
C
VCC
RB
Vout
vo
IC
Vout = VCE / V
cutoff
6.0
ideal
linear region
Slope = A (voltage
gain)
0.2
0.5
0.7
saturation
Vin /V
Vin = total input voltage
Vi = bias (d.c.) voltage
vi = input signal (to be amplified)
Vin = Vi + vi
Vout = total output voltage
Vo = output voltage due to bias input voltage
vo = output signal (amplified)
Vout = Vo + vo
voltage amplification
use linear region only
(suppose Vcc = 6V)
Vout = VCE / V
cutoff
6.0
Middle of linear region
Vo 3V
0.2
linear region
0.5
0.7 Vi
saturation
Vin /V
Proper biasing condition ( 最佳偏壓狀態 )
• adjust the potentiometer ( Vi & IB)
 steady output voltage Vo = 3 V
(the middle of the linear region)
• Without signal generator, (vi = 0)
Vin = Vi &
Vout = Vo (vo = 0)
bias voltage Vi ( 偏壓 ) &
bias current IB偏壓電流
voltage amplification
use linear region only
(suppose Vcc = 6V)
Vout = VCE / V
cutoff
6.0
Middle of linear region
Vo 3V
0.2
linear region
0.5
0.7 Vi
saturation
Vin /V
Vout
Vout = VCE / V
6.0
Vo
t
Vin /V
Vin
t
Vi
The a.c. input vi can then be amplified with
maximum possible amplitude before distortion.
Distortion: range of input/output
voltage is out of the linear region
Vout
Vo
Vout = VCE /
6.
V
0
t
Vin
Vin /V
t
Vi
• 180o out of phase between vi and vo , A is -ve
Vo & Vi: (constant)d.c.
& vi & vo: a.c.
Vout  Vo  v o 
v o
peak value of v o
A



Vin
 Vi  vi 
vi
peak value of vi
vo /vi = A = -  (RL/RB)
For calculating the biasing voltage & biasing
current, use the following equation:
Vin = VBE + IBRB
VCC = ICRL + Vout
IC =  IB
remarks
l capacitor C:
d.c. blocking capacitor ( 隔直流電容 )
large capacitance  block d.c.  a.c. only
l capacitor C  : blocking d.c. (output now)
but it can be omitted if the CRO is set at AC mode
l variation of vi are too large  vo will move into
the non-linear regions  distortions
l RL decreases or RB increases
 smaller A
 wider linear region
P.6 example 1
Best biasing condition: set Vo = 3V
A = -  (RL/RB) = -180 (2.2k/15k) = -26.4
VCC = ICRL + VOUT
6 = IC(2.2k) + 3
IC = 1.3636mA
IB‘ = IC /  = 1.3636 / 180 = 0.0076mA
Vin = (Vi + 0) = VBE + IB’RB
Vi = 0.7 + (0.0076m)(15k) = 0.814V
• In this example, we see that
typically, RB (15k) > RL (2.2k)
• Since IB << IC (IC = IB)
Example 2
Let Vcc = 6V
IB
RB
C
Signal
generator
vi
RB
IC
RL
C
VCC
IB
vo
IB  IB
IC + IB
• set Vo = 3V
• Now
Vcc = VO + ICRL
Vcc = IB’ RB’ + VBE
IC = IB
IC = 1.3636 mA
IB’ = 0.00909mA
Vcc = IB’ RB’ + VBE
6 = (0.00909m x RB’) + 0.6
RB’ = 594k
AL 01-41
Operational amplifier
( Op amp 運算放大器 )
V1: Inverting input
( 反相輸入 )
V2: Non-inverting input
( 非反相輸入 )
 VS:
+VS
V1
V2

Vo
+
VS
The voltage of the power supply
For example: + VS = +15 V,  VS = 15 V
VO = Voltage output
Properties of op amp
1. A very high input impedance (  106-1012  )
It draws tiny current (about 0A) from the
device or circuit supplying its input.
2. A very low output impedance (  100  )
3. The open-loop voltage gain AO 開環電壓增益
VO = Ao (V2  V1)
AO is very high, of the order of 105 .
Ideal op amp:
•
•
•
infinite large input impedance
無限大的輸入阻抗
zero output impedance
零輸出阻抗
infinite large open-loop voltage gain AO
無限大開環電壓增益
I/O voltage transfer characteristic
Vo / V
saturation
+ VS
V
(V2  V1) / mV
V
saturation
 VS
+VS
V1
V2

+
Vo
VS
 V = VS / AO
• If (V2 – V1) > V  VO = VS
• If (V2 – V1) < -V  VO = -VS
• If [ -V < (V2 – V1) < V ]
(linear region)
VO = Ao (V2  V1)
• Since Ao is very large,
V is very small
V << 1mV
• Larger AO
 smaller V
narrow linear region
Comparator ( 比較器 ) as a switch
• if V2  V1＞V
 saturation
• compare two nearly equal voltage
• V2 > V1  Vo = +ve
• V2 < V1  Vo = -ve
98-40
Use of open loop gain Ao is very limited
since it is too large
and the op amp is often saturated.
Negative feedback amplifier ( 負反饋放大器 )
• Closed-loop gain A 閉環電壓增益
feedback resistor
Rf
V1

Vo
V2
+
Advantages of negative feedback
(I)
Predictable & constant voltage gain A
(independent of the intrinsic property
(Ao & Vs) of the op amp)
(II)
More linear amplification
(linear region of greater width)
(III) The voltage gain is stable for a wider range
of frequencies of input a.c.
Negative feedback
• We always use the assumption
(I)
V2  V1
(II)
the current i flow between the
inverting &non-inverting input 
0
Inverting amplifier
反相放大器
Ii
V1
VP  VQ
VQ = 0  VP  0
Now Vi  VP = Ii Ri
Vi = Ii Ri &
…….…(1)
Rf
If
Ri VP i

VQ
+
virtual ground ( 虛接地 )
& VP  VO = If Rf
 VO = If Rf
VO
Vi = Ii Ri &
 VO = If Rf
…….…(1)
since i  0

Ii = If + i  If
….……(2)
(1) & (2), Vi/Ri = VO/ Rf
closed loop voltage gain A 閉環電壓增益 :
Since Ii  If
VO
I f Rf
Rf
A


Vi
I i Ri
Ri
• A depends only on Rf and Ri
& is independent of Ao & Vs
• If Rf = Ri  A = 1
• it acts as an inverter反相器
Summing amplifier 加法放大器
V1
V2
V3
R1
I1
R2 I2
R3 I3
Rf
If
VP i
VQ
Vout
VP  VQ = 0
Vi  VP = Ii Ri (i = 1, 3, 3) & VP  VO = If Rf
Vi /Ri = Ii
&  VO/Rf = If
Vi /Ri = Ii &  VO/Rf = If
i=0
SIi = If + i  If
(1) & (2),
…..(1)
…..(2)
 V1 V2 V3 
VO
  
 
Rf
 R1 R2 R3 
If R1 = R2 = R3 = Rf,
Vo = - (V1 + V2 + V3)
97- 42
+15
+15
-15
0
+5
0
-5
-15
+5 V
-5 V
vo  [5  2  5]  5 V
Non-inverting amplifier 同相放大器
VP  VQ = Vi
VP

VQ
+
i
Vi
If
Rf
i
I
R
VO
VP  VQ = Vi
VO  VP = If Rf
&
(VO  Vi)/Rf = If
&
i=0
VP  0 = IR
Vi/R = I

I = If  i = If

Vi VO  Vi

R
Rf

VO
Rf
1 
Vi
R
closed loop voltage gain:
Rf
A  1
R
If Rf = 0 and R =  (very large)
then A = 1
voltage follower ( 電壓跟隨器 )
Though the output voltage is the same as the
input voltage, its output current is very large.
Owing to its high input but low output
impedance, a voltage follower can be
constructed into an electrometer.
Input-output current characteristic
of a voltage follower
VP

Ii
VQ
Vi
VO = VP = VQ = Vi
r
IO
+
RL
VO
V
I
R
O
O
L
For open voltage gain, V  VQ  VP 

A0
A0
For input resistance,
V  VQ  VP  I i r
I O RL
 Iir

A0
A0 r
Ii
 IO 
RL
For A0  105 , r  106  , RL = 10 k ,
IO/Ii  107
Though voltage gain A is 1, the current is amplified.
00 - 42