electronics system in engineering for learning

this is elctronics subjects

1. Electronics Engineering II
Course Code: EEEG 214
Credit Hours: 3
1/6/22 Asst Prof Kamal Chapagain, KU
Course Title:
Objective: To expose the students to the in-depth idea
regarding the electronic circuit and analysis.

2. Total Chapters: 6
•Feedback System.
•Oscillators and Waveform
Generators.
•Non-linear Analog Circuits.
•Logic Circuits.
•Integrated Circuit
Fabrication.
•Pulse Generation and Wave
Shaping Circuits.
1/6/22 Asst Prof Kamal Chapagain, KU

3. Feedback: Electronics ckt
•The phenomenon of feeding a portion of the
output signal back to the input circuit is known as
feedback.
•Positive feedback or regenerate feedback:
•Negative feedback or degenerative feedback:
•Positive feedback:
•In positive feedback, the feedback energy (voltage or
currents), is in phase with the input signal and thus
aids it.
•Positive feedback increases gain of the amplifier also
increases distortion, noise and instability.
•Because of these disadvantages, positive feedback is
seldom employed in amplifiers. But the positive
feedback is used in oscillators.


1/6/22 Asst Prof Kamal Chapagain, KU

4. •Negative feedback: the feedback energy
(voltage or current), is out of phase with
the input signal and thus opposes it.
• Negative feedback reduces gain of the
amplifier. It also reduce distortion, noise and
instability.
•This feedback increases bandwidth and
improves input and output impedances.
•Due to these advantages, the negative
feedback is frequently used in amplifiers.

1/6/22 Asst Prof Kamal Chapagain, KU
The input signal Vs is applied to a mixer
network, where it is combined with a feedback
signal Vf. The difference of these signals Vi is
then the input voltage to the amplifier. A
portion of the amplifier output Vo is connected
to the feedback network, which provides a
reduced portion of the output as feedback
signal to the input mixer network
Feedback: Electronics ckt

5. Derivation of general expression: feedback
•
1/6/22 Asst Prof Kamal Chapagain, KU

6. The condition for oscillation: Barkhausen criterion

•Conditions which are required to be satisfied to
operate the circuit as an oscillator are called as
“Barkhausen criterion” for sustained oscillations.
•The Barkhausen criteria should be satisfied by an
amplifier with positive feedback to ensure the
sustained oscillations.
•For an oscillation circuit, there is no input signal “Vs”,
hence the feedback signal Vf itself should be
sufficient to maintain the oscillations.
1/6/22 Asst Prof Kamal Chapagain, KU

7. Assignment: What is the Effect of feedback
on:
•Overall gain,
•Stability
•Sensitivity
•Visit: https://www.tutorialspoint.com/control_systems/control_systems_feedback.htm

1/6/22 Asst Prof Kamal Chapagain, KU
•Types of Oscillators
•Feedback oscillators(using +ve feedback)
•Relaxation oscillators (Due to charge/discharge of capacitors in the ckt)
•High frequency oscillators (LC oscillators)
•Hartley, Colpitts, crystal
•Low frequency oscillators (RC oscillators)
•RC phase shift oscillators
•Wein bridge oscillators

8. Basic LC oscillator
1/6/22 Asst Prof Kamal Chapagain, KU
•The circuit consists: Inductive coil, L and a capacitor, C.
•When switch moves position A: Capacitor is charged up to the DC supply voltage, and
when the capacitor is fully charged, lets changes switch to position B.
•The charged capacitor begins to discharge itself through the coil. The voltage across C get
down and current through the coil begins to rise.
•This rising current sets up an electromagnetic field in the coil which resists this flow of
current.
•When the capacitor, C is completely discharged the electrostatic field is now stored in the
inductive coil, L as an electromagnetic field around the coils windings.
•As there is now no external voltage in the circuit to maintain the current within the coil, it starts to fall as the electromagnetic
field begins to collapse. A back emf is induced in the coil (e = -Ldi/dt) keeping the current flowing in the original direction.
•This current charges up capacitor, C with the opposite polarity to its original charge. C continues to charge up until the current
reduces to zero and the electromagnetic field of the coil has collapsed completely.
•The energy originally introduced into the circuit through the switch, has been returned to the capacitor which again has an
electrostatic voltage potential across it, although it is now of the opposite polarity. The capacitor now starts to discharge again
back through the coil and the whole process is repeated. The polarity of the voltage changes as the energy is passed back and
forth between the capacitor and inductor producing an AC type sinusoidal voltage and current waveform.
•This process then forms the basis of an LC oscillators tank circuit and theoretically this cycling back and forth will continue
indefinitely. However, things are not perfect and every time energy is transferred from the capacitor, C to inductor, L and back
from L to C some energy losses occur which decay the oscillations to zero over time.
•Then in a practical LC circuit the amplitude of the oscillatory voltage decreases at each half cycle of oscillation and will eventually
die away to zero. The oscillations are then said to be “damped” with the amount of damping being determined by the quality or
Q-factor of the circuit.

9. 1/6/22 Asst Prof Kamal Chapagain, KU

10. 1/6/22 Asst Prof Kamal Chapagain, KU

11. •The frequency of the oscillatory voltage depends upon the value of the
inductance and capacitance in the LC tank circuit.
•We now know that for resonance to occur in the tank circuit, there must be a
frequency point were the value of X
C
, the capacitive reactance is the same as
the value of X
L
, the inductive reactance ( X
L
= X
C
) and which will therefore
cancel out each other out leaving only the DC resistance in the circuit to
oppose the flow of current.
1/6/22 Asst Prof Kamal Chapagain, KU
Basic LC oscillator

12. Resonance Frequency
1/6/22 Asst Prof Kamal Chapagain, KU
•Where:
•L is the Inductance in Henries
•C is the Capacitance in Farads
•ƒ
r
is the Output Frequency in Hertz

13. RC Oscillator and its criteria
In an Resistance-Capacitor (RC) Oscillator circuit the input is shifted
180
o
through the feedback circuit returning the signal out-of-phase
and 180
o
again through an inverting amplifier stage to produces the
required positive feedback. This then gives us “180
o
+ 180
o
= 360
o
” of
phase shift which is effectively the same as 0
o
, thereby giving us the
required positive feedback. In other words, the total phase shift of the
feedback loop should be “0” or any multiple of 360
o
to obtain the
same effect.
Asst Prof Kamal Chapagain, KU
•The circuit on the left shows a single
resistor-capacitor network whose
output voltage “leads” the input
voltage by some angle less than 90
o
.
•In a pure or ideal single-pole RC
network, it would produce a maximum
phase shift of exactly 90
o
, and because
180
o
of phase shift is required for
oscillation, at least two single-poles
networks must be used within an RC
oscillator design.

14. RC Oscillator and its criteria
•However in reality, it is difficult to obtain exactly 90
o
of
phase shift for each RC stage. When R=0 ohm, then
only phase shift = 90
o

•Therefore, for 180
o
phase, more than two RC stages
are cascaded together.
•If each stage produce 60
o
, we need 3 stages. Setting
different values for R, C and f we can get phase of 60
o

•The amount of actual phase shift in the circuit depends
upon the values of the resistor (R) and the capacitor
(C), at the chosen frequency of oscillations with the
phase angle ( φ ) being given as,
1/6/22 Asst Prof Kamal Chapagain, KU
Where: X
C
is the Capacitive Reactance of the capacitor, R is the
Resistance of the resistor, and ƒ is the Frequency.

15. Basic RC oscillator circuit
•The basic RC Oscillator which is also known as a Phase-shift Oscillator,
produces a sine wave output signal using regenerative feedback obtained
from the resistor-capacitor (RC) ladder network. This regenerative
feedback from the RC network is due to the ability of the capacitor to
store an electric charge, (similar to the LC tank circuit).
•This resistor-capacitor feedback network can be connected as shown
above to produce a leading phase shift (phase advance network) or
interchanged to produce a lagging phase shift (phase retard network) the
outcome is still the same as the sine wave oscillations only occur at the
frequency at which the overall phase-shift is 360
o
.
•By varying one or more of the resistors or capacitors in the phase-shift
network, the frequency can be varied and generally this is done by
keeping the resistors the same and using a 3-ganged variable capacitor
because capacitive reactance (X
C
) changes with a change in frequency as
capacitors are frequency-sensitive components. However, it may be
required to re-adjust the voltage gain of the amplifier for the new
frequency.
1/6/22 Asst Prof Kamal Chapagain, KU
If the three resistors, R are equal in value, that is R
1
= R
2
= R
3
,
and the capacitors, C in the phase shift network are also equal
in value, C
1
= C
2
= C
3
, then the frequency of oscillations
produced by the RC oscillator is simply given as:

16. Derivation
1/6/22 Asst Prof Kamal Chapagain, KU