1. ELECTRONICS II 3rd SEMESTER ELECTRICAL

3. Cass–A operation
For maximum swing ( +ve and –ve), transistor is biased such that the Q point is at centre of the load line.
The transistor conducts for a full cycle of the input signal

4. Theoretical maximum efficiency of class-B amplifiers

5. Cass–C operation
B – E junction is reverse-biased to obtain Q-point beyond cut-off.
Transistor conducts for less than half a cycle of input signal
Tuned circuit is required.
Used for RF amplifier.
Efficiency > 78.5%

6. Oscillator
Oscillator is an electronic circuit that generates a periodic waveform on its output without an external signal source. It is used to convert dc to ac.
Oscillators are circuits that produce a continuous signal of some type without the need of an input.
These signals serve a variety of purposes.
Communications systems, digital systems (including computers), and test equipment make use of oscillators

7. Need of an Oscillator
An oscillator circuit is capable of producing ac voltage of desired frequency and waveshape.
To test performance of electronic circuits, it is called signal generator.
It can produce square, pulse, triangular, or sawtooth wave shape.
High frequency oscillator are used in broadcasting.
Microwave oven uses an oscillator.
Used for induction heating and dielectric heating.

8. The Oscillator

9. Types of Oscillator RC Oscillator - Wien Bridge Oscillator
- Phase-Shift Oscillator
2. LC Oscillator - Crystal Oscillator
3. Relaxation Oscillator

10. Wien-Bridge Oscillator
It is a low frequency oscillator which ranges from a few kHz to 1 MHz.
Structure of this oscillator is

11. Phase-Shift Oscillator
The phase shift oscillator utilizes three RC circuits to provide 180º phase shift that when coupled with the 180º of the op-amp itself provides the necessary feedback to sustain oscillations.

12. Crystal Oscillator
The crystal appears as a resonant circuit (tuned circuit oscillator).
The crystal has two resonant frequencies:
Series resonant condition
RLC determine the resonant frequency
The crystal has a low impedance
Parallel resonant condition
RLC and CM determine the resonant frequency
The crystal has a high impedance
The series and parallel resonant frequencies are very close, within 1% of each other.

13. What is the IC 555?
The IC 555 is an 8-pin Integrated Circuit (IC) that is capable of producing accurate time delays and/or oscillations.
DIP chip (Dual-Inline package)

14. What is an Op-Amp?
An Operational Amplifier (known as an “Op-Amp”) is a device that is used to amplify a signal using an external power source
Op-Amps are generally composed of:
Transistors, Resistors, Capacitors =

15. Positive power supply (Positive rail)
Terminals on an Op Amp
Positive power supply (Positive rail)
Non-inverting
Input terminal
Output terminal
Inverting input
terminal
Negative power supply
(Negative rail)

16. Typical Op Amp Parameters
Variable
Typical Ranges
Ideal Values
Open-Loop Voltage Gain A
105 to 108 ∞
Input Resistance Ri
105 to 1013 W
∞ W
Output Resistance Ro
10 to 100 W
0 W
Supply Voltage
Vcc/V+
-Vcc/V-
5 to 30 V
-30V to 0V
N/A

17. Non-Inverting Op-Amp Amplifies the input voltage by a constant
Closed loop op-amp
Voltage input connected to non-inverting input
Voltage output connected to inverting input through a feedback resistor
Inverting input is also connected to ground
Non-inverting input is only determined by voltage output

18. Inverting Op-Amp Vout=K(V+-V-) V-=Vout(Rin/(Rin+Rf))+Vin(Rf/(Rin+Rf))
V-=(VoutRin+VinRf)/(Rin+Rf)
Vout=K(0-V-)
Vout=-VinRf/[(Rin+Rf)/K+(Rin)]
Vout=-VinRf/Rin

19. Integrating Op-Amp Integrates the inverted input signal over time
Closed loop op-amp
Voltage output is connected to inverting input through a capacitor
The resistor and capacitor form an RC circuit
Magnitude of the output is determined by length of time voltage is present at input
The longer the input voltage is present, the greater the output

20. Op Amps Applications Audio amplifiers Instrumentation amplifiers
Speakers and microphone circuits in cell phones, computers, mpg players, boom boxes, etc.
Instrumentation amplifiers
Biomedical systems including heart monitors and oxygen sensors.
Power amplifiers
Analog computers
Combination of integrators, differentiators, summing amplifiers, and multipliers