Term Roadmap :
• Introduction to Signal Processing
• Differentiating and Integrating Circuits (OpAmps)
• Clipping and Clamping Circuits(Diodes)
• Design of analog filters
• Sinusoidal Oscillators
• Multivibrators
• Sampling and Quantization techniques of analog signals
• DACs and ADCs
• Data Acquisition Systems
• Introduction to discrete time transform and DSP
• The Z transform
• Design of Digital Filters
Materials Types
1. INSULATORS
• An INSULATOR is any material that inhibits
(stops) the flow of electrons (electricity).
• An insulator is any material with 5 to 8 free
electrons in the outer ring. Because, atoms
with 5 to 8 electrons in the outer ring are held
(bound) tightly to the atom, they CANNOT be
easily moved to another atom nor make room
for more electrons.
• Insulator material includes glass, rubber, and
plastic
Materials Types
2. CONDUCTORS
•A CONDUCTOR is any material that easily
allows electrons (electricity) to flow.
•A CONDUCTOR has 1 to 3 free electrons in
the outer ring. Because atoms with 1 to 3
electrons in the outer ring are held (bound)
loosely to the atom, they can easily move to
another atom or make room for more electrons.
•Conductor material includes copper and gold
Materials Types
3. SEMICONDUCTORS
•Any material with exactly 4 free electrons in
the
outer
orbit
are
called
SEMICONDUCTORS.
•A semiconductor is neither a conductor or
insulator.
• Semiconductor material includes carbon,
silicon, and germanium.
•These materials are be used in the
manufacturer of diodes, transistors, and
integrated circuit chips.
•
•
•
•
Semiconductor Diode
Diode is formed by bringing these two material together p- and n-type.
Holes diffuse from the p side to the n side, leaving behind negatively
charged immobile negative ions.
Electrons diffuse from the n side to the p side, leaving behind positively
charged immobile positive ions.
Electrons and holes at joined region will combine, resulting in a lack of
carriers in the region near the junction (depletion region)
Reverse-Bias Condition (VD < 0V)
Reverse-biased p-n junction
Reverse-Bias Condition (VD < 0V)
•
•
•
•
The number of positive ions in the depletion region of n-type
will increase due to large number of free electrons drawn to
the positive potential.
The number of negative ions will increase in p-type resulting
widening of depletion region.
This region established great barrier for the majority carriers
to overcome, resulting Imajority = 0
A very small amount of reverse current does flow, due to
minority carriers diffusing from the (p/n) regions into the
depletion region and drifting across the junction.
Forward-Bias Condition (VD > 0V)
Forward-biased p-n junction
Forward-Bias Condition (VD = 0V)
• A semiconductor diode is forward-biased when the
association p-type and positive voltage and n-type
and negative voltage has been established.
• The application of forward-bias potential will pressure
the electrons in n-type and hole in p-type to
recombine with ions near the boundary and reduce
the width of depletion region
• The reduction in width of depletion region has
resulted in a heavy majority flow across the junction
Semiconductor Diodes
Figure 3.39 Simplified physical structure of the junction diode. (Actual geometries are given in Appendix A.)
Circuit
symbol
Diodes
Several types of diodes. The scale is centimeters
The i–v characteristic of a silicon diode.
Figure 3.7 The i– characteristic of a silicon junction diode.
Figure 3.8 The diode i– relationship with some scales
expanded and others compressed in order to reveal details.
The i–v characteristic of a silicon diode.
•
•
The Forward-Bias region:-
In the forward region the i- v relationship is closely approximated by…..
kv
Tk
i I s (e
•
1)
Is …….the reverse saturation current ( scale current)
– K = Boltzmann`s constant = 1.38*10-23 joules / kelvin
– Tk= the absolute temperature in kelvins = 273 + temperature in °C
The i–v characteristic of a silicon diode.
•
The Reverse-Bias region:-
•
The exponential term becomes negligibly small compared to unity, and the diode current
becomes…..
i Is
•
That is, the current in the reverse direction is constant and equal to Is which tends to
zero.
•
The Breakdown Region:-
•
The breakdown region is entered when the magnitude of the reverse voltage exceeds a
threshold value that is specific to the particular diode, called the breakdown voltage.
Ideal Diode
Figure 3.1 The ideal diode: (a) diode circuit symbol; (b) i– characteristic;
(c) equivalent circuit in the reverse direction; (d) equivalent circuit in the
forward direction.
Figure 3.2 The two modes of operation of
ideal diodes and the use of an external circuit
to limit the forward current (a) and the reverse
voltage (b).
Modeling the diode forward characteristic
The Piecewise-linear Model
Figure 3.13 Piecewise-linear model of the diode forward characteristic and its
equivalent circuit representation.
Figure 3.12 Approximating the diode forward
characteristic with two straight lines: the piecewiselinear model.
Figure 3.14 The circuit of
Fig. 3.10 with the diode
replaced with its piecewiselinear model of Fig. 3.13.
Modeling the diode forward characteristic
The Piecewise-linear Model
Example:
Given: VDD = 5V, VDO= 0.65, rD = 20 ,R= 1K
Thus
ID 5 0.65
4.26mA
1 0.02
VD = VDO+IDrD
= 0.65+4.26x0.02=0.735V
Modeling the diode forward characteristic
The Constant-voltage-drop Model
Figure 3.15 Development of the constantvoltage-drop model of the diode forward
characteristics. A vertical straight line (B) is used
to approximate the fast-rising exponential.
Observe that this simple model predicts VD to
within 0.1 V over the current range of 0.1 mA to
10 mA.
Figure 3.16 The constant-voltage-drop model of the diode forward
characteristics and its equivalent-circuit representation.
Modeling the diode forward characteristic
The Ideal Diode Model
Figure 3.1 The ideal diode: (a) diode circuit symbol; (b) i– characteristic; (c) equivalent circuit in the
reverse direction; (d) equivalent circuit in the forward direction.
Operation in The reverse Breakdown
Region- Zener Diodes
Figure 3.20 Circuit symbol for a zener diode.
Figure 3.22 Model for the zener diode.
Figure 3.21 The diode i– characteristic with the breakdown region shown in some
detail.
Operation in The reverse Breakdown
Region- Zener Diodes
Example: Find I ?
Figure 3.23 (a) Circuit for Example 3.8. (b) The circuit with the zener diode replaced with its equivalent circuit model.
Diode Applications
AND/OR Gates
„
AND and OR gates represent basic components of computers that
are used to implement Boolean algebra.
OR-Gate
AND-Gate
1
2
3
1
2
3
0
0
0
0
0
0
0
1
1
0
1
0
1
0
1
1
0
0
1
1
1
1
1
1
If logic “1” is represented by +10 (+5) V and logic “0” is
represented by 0 V, the OR and the AND gates can be
represented by the following diode combinations;
AND/OR Gates
„
„
For the OR gate;
– D1ON
– D2 OFF
– V0=10V ( logic 1)
For the AND gate;
– D1 OFF
– D2 ON
– V0=0V ( logic 0)
Diodes Applications: Rectifier Circuits
Figure 3.24 Block diagram of a dc power supply.
Sinusoidal Inputs; Half-wave Rectification
(Ideal diode Model)
• So far, we have considered time invariant signals only (DC).
• Now, diode circuit analysis will be extended to include circuits containing time
varying signals (AC).
• The simplest diode application that uses AC signals is the HWR signal shown.
• To simplify the analysis, we’ll assume that the diodes used are ideal.
• Note that, the DC content of the input waveform is zero, Why?
• During time interval t=0 T/2, diode is ON.
• Since we are using an ideal diode model, v0=vi.
• During the time interval t=T/2 T, diode is OFF; v0=0.
• Now, what is the value of the DC level in the output waveform? (Vdc=0.318Vm)
5.0V
0V
-5.0V
0s
V(R5:2)
1.0s
V(V5:+)
2.0s
Time
HWR with Const Voltage Drop Diode Model
• In case of using the constant voltage drop diode model, during the conduction
period diode will be replaced with a constant voltage source VD0.
• Thus, the peak of the output waveform will decrease from Vs by VD0.
• In addition, the conduction period of the diode will be slightly less than T/2.
• In this case, the DC content of the output waveform becomes;
• Vdc0.318(Vs-VD0)
(Note:0.318Vs =Vs/) (Vs i.e Vm , VD0 i.e VT)
• Peak Inverse Voltage (PIV)
• Definition: PIV is the value of the maximum reverse voltage that is expected
to apply to the diode in during its operation.
• PIV: Peak Inverse Voltage in this case = Vs, Thus, PIVrating>Vs
The rectifier with a filter capacitor
The rectifier with a filter capacitor
Full-wave Rectifier
• DC level can be improved to 100% of that obtained in HWR, by using the full-wave
rectifier configuration shown.
• For t=0ÆT/2, D1 and D2 ON while D3, and D4 OFF.
• For t=T/2ÆT, D3, D4 ON, while D1 and D2 OFF.
• As seen form the waveform generated, the DC level for that configuration is twice that of
the HWR.
• Vdc(FWR)=2
Vdc(HWR)= 2
0.318Vs , ideal diode model.
•
=2
0.318(Vs-2VD0) simplified
• PIV|rating>Vs
Center Tapped Transformer FWR
•
•
•
•
For t=0ÆT/2, D1 ON while D2, OFF.
For t=T/2ÆT, D2 ON, while D1, OFF
PIV|rating>2Vs
Example 2.19
Clipper Circuits
Clipper circuit is the circuit which clip off a portion of
the input signal without distorting the remaining
part of the signal
Figure 3.33 Applying a sine wave to a limiter can result in clipping off its two peaks.
Clippers
•
•
•
•
Clipper circuits is used to remove one part of the signal without distorting the remaining part.
The orientation of the diode determines the part of the signal that is removed, while the value
of the DC controls the level of clipping.
It is usually consists of , a diode, a resistance and a DC source.
Clippers have two major configurations;
– Series Configuration, where the diode is connected in series with the the source.
– Parallel Configuration; where the diode is connected in parallel with the output port.
• Single Side Clippers
Double Side Clippers
• Series Clippers
10V
0V
-10V
0s
100ms
V(RL:2)
V(Vs:+)
200ms
300ms
400ms
Time
– The output voltage is given by KVL as;
– vo= vs-V- VD such that the voltage at the diode input has to be greater than VT for the
diode to conduct. Otherwise, the diode will be off and vo will be zero.
Parallel Clippers
Upper Side Clippers:
10V
0V
-10V
vi
v0 vD V
0s
V(V:+)
100ms
V(RL:2)
200ms
300ms
400ms
500ms
Time
if D is OFF
if D is ON
5.0V
Lower Side Clipper
0V
-5.0V
0s
V(R2:2)
50ms
V(V1:+)
100ms
150ms
200ms
250ms
300ms
Time
5.0V
Double Side Clipper
0V
Lec(3-1)
-5.0V
0s
V(V10:+)
50ms
V(V1:+)
100ms
٣٤
150ms
200ms
Time
250ms
Clipper Circuits
Example:
Clampers
• A clamping circuit is the circuit that is used to clamp a signal to a certain
DC level.
• It must contain a capacitor, a diode and a resistive element.
• The value of the discharging time constant of the capacitor, dis=RC>>T/2
has to be large enough to ensure that the capacitor doesn’t discharge during
the OFF period of the diode.
• The very small resistance of the diode RD makes the charging time constant
ch=RDC so small that its can be considered that the diode charges in zero
time.
Clampers
• Rules:
– The Direction of the diode’s arrow determines whether the signal is
clamped up or down.
– The value of the DC source connected to the diode’s anode determines
the max or the min of the clamped signal respectively.
• Operation
– For t=0ÆT/2, D is ON
–
–
–
–
Resistance R1 is
short-circuited by the diode.
C charges to Vm in
zero time (theoretically).
For t=T/2ÆT,D is OFF.
C discharges through R1
The Value of the output voltage
is –[Vs(Vm)+Vc(Vm)]
Clampers
• Rules:
– The Direction of the diode’s arrow determines
whether the signal is clamped up or down.
– The value of the DC source connected to the
diode’s anode determines the max or the min of
the clamped signal respectively.
• Operation
Example:
VOLTAGE MULTIPLIER CIRCUITS
• Voltage multiplier circuits are used to maintain low transformer peak
voltage and stepping up the voltage to 2, 3,or 5 times this value
• Voltage Doubler ( Half-Wave)
During +ive half cycle, D1 ON, D2 OFF, C1 charges to
+Vm
– During -ive half cycle, D1 OFF, D2 ON, C2 charges to
+2Vm as following;
-VC2+Vc1+Vm=0
VC2=Vc1+Vm=2Vm
The Voltage Doublers
Figure 3.38 Voltage doubler: (a) circuit; (b) waveform of the voltage across D1.
Dr. Mohamed Hassan
Full-wave Voltage Multiplier
• During (+)ive half cycle, D1 ON, D2 OFF,
C1 charges to +Vm
• During (-)ive half cycle, D1 OFF, D2 ON,
C2 charges to +Vm.
• So the total output voltage applied to the
load is 2Vm.
Voltage Tripler and Quadrupler
• During (+)ive half cycle , D1 ON, C1
charges to Vm.
• During (-)ive half cycle , D1 OFF, C2
charges to 2Vm.through C1 and the
secondary winding of transformer.
• During the next (+)ive half-cycle, D3
conducts, and C2 charges C3 to 2Vm
Thank You