SHANTILAL SHAH ENGINEERING COLLEGE ELECTRICAL DEPARTMENT

BE ELECTRICAL SEM-3 ANALOG ELECTRONICS OSCILLATOR Guided by : A.M.Upadhyay sir  Submitted by:  Gohil Uma V.( )  Solanki Krupali K.( )  Damor Divyangini L.( )  Tuvar Beena B.( )  Zala Disha B.( )

 What we will going to learn? Define the basic oscillator circuit Identify the conditions for oscillation to occur Identify input and output characteristics Identify common uses of the oscillator 

Introduction Introduction 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

An oscillator is a circuit that produces a repetitive signal from a dc voltage. The feedback oscillator relies on a positive feedback of the output to maintain the oscillations. The relaxation oscillator makes use of an RC timing circuit to generate a nonsinusoidal signal such as square wave Sine wave Square wave Sawtooth wave

Ref: HKNEE3110 Oscillator6  Integrant of Linear Oscillators For sinusoidal input is connected “Linear” because the output is approximately sinusoidal A linear oscillator contains: - a frequency selection feedback network - an amplifier to maintain the loop gain at unity

Ref: HKNEE3110 Oscillator7  Basic Linear Oscillator and If V s = 0, the only way that V o can be nonzero is that loop gain A  =1 which implies that (Barkhausen Criterion)

Overview of the Oscillator  One of the basic building blocks of electronics  Input is a direct current (DC) power source  Output is alternating current (AC)  Can generate sub-audible frequencies or very high frequencies  Most oscillators are amplifiers with feedback

 Oscillation: an effect that repeatedly and regularly fluctuates about a mean value  Oscillator: circuit that produces oscillation  Characteristics: frequency, amplitude, distortion, wave-shape, stability

Amplifiers as Oscillators? Most amplifiers will oscillate when conditions are correct ◦Example: Too high of a volume on public address system = loud noise and squeals that are the result of acoustic waves traveling from the speakers to the microphone The result is oscillation

Electrical Feedback Practical oscillators use electrical feedback to produce oscillation Feedback circuits use resistors, capacitors, coils, or transformers to connect a portion of the output signal back to the input of the amplifier

 Basic principles for oscillation

 Types of oscillators 1. RC oscillators ◦Wien Bridge ◦Phase-Shift 2. LC oscillators ◦Hartley ◦Colpitts ◦Crystal 3. Unijunction / relaxation oscillators

 RC Oscillators RC feedback oscillators are generally limited to frequencies of 1 MHz or less. The types of RC oscillators that we will discuss are the Wien-bridge and the phase-shift

 LC Oscillators Use transistors and LC tuned circuits or crystals in their feedback network. For hundreds of kHz to hundreds of MHz frequency range. Examine Colpitts, Hartley and crystal oscillator.

 Feedback and Amplifier Gain Conditions for Oscillation Feedback alone does not promise oscillation There is always some loss in the feedback circuit Amplifier gain must be greater than this loss Feedback must be in-phase

In-phase Feedback In-phase feedback is also called regenerative feedback or positive feedback When the original amplifier input and output signals are not in-phase, the feedback circuit is used to reverse the phase

Input Characteristics Steady source of direct current (DC) In many applications, the DC source requires a filter

Output Characteristics Amplitude Frequency Waveform type Stability On some oscillators, the capability to change frequency

Oscillator Amplitude Usually determined by the gain available from the amplifier Supply voltage and circuit losses affect amplitude

Oscillator Frequency Frequency of operation is normally determined by the feedback circuit Common feedback circuits used to determine oscillator frequency include: ◦ crystals ◦ resistor and capacitor networks (RC) ◦ coil and capacitor networks (LC) {tank circuit}

Waveform Type Generally, determined by: ◦Feedback circuitry ◦Output filter circuitry ◦Amplifier gain, or ◦Changes to input voltage May be sinusoidal (sine wave), square wave, or triangular wave

Oscillator Stability Sometimes referred to as a stable oscillator Source of a signal with consistent amplitude Source of a signal with consistent frequency

 Ability to Change Frequency Oscillators sometimes have the ability to change frequencies Crystal oscillator frequency is controlled by changing the crystal ◦Crystals are usually cut from quartz to generate a specified frequency when operating

Typical Uses of the Oscillator Radio and television stations require oscillators to develop the basic signal to transmit their information

Cell phones, electronic keyboards, and remote controls use oscillators to produce the required frequencies for operation

Digital devices such as computers, watches, calculators, and iPods all require oscillators to generate the rectangular waveform required for operation

Typical Uses of the Oscillator Variable oscillators, known as signal generators, are used to generate frequencies and waveforms needed for troubleshooting and the testing of electronic equipment

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