* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download ppt - EC - Unit 6 - sine wave -1
Schmitt trigger wikipedia , lookup
Cavity magnetron wikipedia , lookup
Oscilloscope history wikipedia , lookup
Electronic engineering wikipedia , lookup
Switched-mode power supply wikipedia , lookup
Operational amplifier wikipedia , lookup
Time-to-digital converter wikipedia , lookup
Flexible electronics wikipedia , lookup
Spark-gap transmitter wikipedia , lookup
Opto-isolator wikipedia , lookup
Integrated circuit wikipedia , lookup
Mathematics of radio engineering wikipedia , lookup
Atomic clock wikipedia , lookup
Negative feedback wikipedia , lookup
Rectiverter wikipedia , lookup
Zobel network wikipedia , lookup
Negative-feedback amplifier wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Equalization (audio) wikipedia , lookup
Crystal radio wikipedia , lookup
Superheterodyne receiver wikipedia , lookup
Valve RF amplifier wikipedia , lookup
Phase-locked loop wikipedia , lookup
Radio transmitter design wikipedia , lookup
Regenerative circuit wikipedia , lookup
Index of electronics articles wikipedia , lookup
Part 1 Unit 6 Sinusoidal Oscillators, Waveshaping Circuits Objectives: • Sinusoidal Oscillators – – – – – – – Classification of oscillators Conditions for oscillations Barkhausen’s criteria Types of oscillators Crystal oscillators Voltage-controlled oscillators Frequency stability • Wave-shaping circuits – – – – RC, RL low-pass & high-pass circuits RC, RL integrator & differentiator circuits Multivibrators IC Multivibrators Sinusoidal Oscillators: Classification: Oscillator (AC generating circuits) Sinusoidal: Generate sine wave Non-Sinusoidal (Multivibrators): Generate square wave or pulsed waveforms TON << TOFF 12.2 Conditions for oscillations: Barkhausen's Criterion Types of feedback systems: • Negative feed back system • Positive feed back system --------Notes: β is gain of frequency selective feedback network, which uses resonant circuit. Negative feedback system: Positive feedback system: Barkhausen's Criterion: Initialization of oscillations: • Generation of oscillations is initialized due to some inevitable noise at input • The amplified output due to noise has all frequency components • Feedback network is frequency selective • Barkhausen’s criterion is satisfied • Oscillations start 12.3 Types of oscillators: • RC oscillators • LC oscillators • Crystal oscillator RC oscillators: • A single RC or RL section provides a maximum of 90° phase shift • Multiple RC sections are used to provide the required phase shift – 3 RC sections 3 x 60° =180° • CE amplifier 180° • Total 180 + 180 = 360° LC oscillators: • A single LC section provides 180° • CE amplifier provides 180 ° • Total 360 ° 15.15 Crystal oscillator: • A quartz crystal with the desired value of the resonant frequency forms the frequencyselective feedback network • More accuracy and stability AC equivalent circuit of Quartz crystal: crystal AC equivalent circuit Resonant frequencies: • Series resonant frequency: 1 fs = -------------------2 Π LCS • Parallel resonant frequency: 1 fp = -------------------2 Π LCp Where Cp = (CM x CS) / (CM + CS) in the above figure Crystal controlled Colpitt oscillator: Resonant / tank circuit Crystal in feedback path to control frequency Crystal based Colpitt oscillator: Resonant / tank circuit Crystal in resonant / tank track to decide frequency 12.16 Voltage controlled oscillator (VCO): • A VCO is an oscillator circuit in which the frequency can be varied by an applied voltage • This is achieved by “varicap”, whose capacitance varies with applied voltage. • Varicap is used in tank circuit, which determines frequency Voltage-controlled Hartley oscillator: •Varicap used as voltage controlled capacitance in resonant / tank circuit •FET used as common-drain amplifier (Av little < 1) •Feedback factor β is large •To avoid noise effect 2 varicaps are used •Fine tuning the frequency is easy with VCO Feedback path 12.17 Frequency stability: • Oscillators ability to maintain constant frequency, for as long a period as possible • Frequency depends on: (large set of elements) – Circuit components – Stray elements (inter-electrode reactance) – Supply voltages – Active device’s characteristics • But largely frequency depends on RC or LC values (small set of elements) Frequency stability criterion: θ=phase-shift Ω=2Πf=frequency • A small set of elements (RC / RL) introduces a large change of phase-shift dθ for a given change in frequency dω, then higher the value of dθ ------, dω more will be the dependence on the these (RC / RL) circuit features • When dθ -----dω approaches infinity, ω is independent of other circuit features (large set of elements) • More the above ratio more the stability 13.1 Basic RC low pass circuit: Xc = R 1 XC = ----------------2Πf C Step & pulse response of LP circuit: 13.2 RC low pass circuit as integrator: Basics / fundas: 1. C=Q / V C= dq / dv ---- in integral form 2. I=Q / T i = dq / dt from 1 dv = dq / C from 2 = (1/C) i dt 1 v = ---- ∫ i dt C Positive feedback system: Barkhausen's Criterion: Initialization of oscillations: • Generation of oscillations is initialized due to some inevitable noise at input • The amplified output due to noise has all frequency components • Feedback network is frequency selective • Barkhausen’s criterion is satisfied • Oscillations start 12.3 Types of oscillators: • RC oscillators • LC oscillators • Crystal oscillator RC oscillators: • A single RC or RL section provides a maximum of 90° phase shift • Multiple RC sections are used to provide the required phase shift – 3 RC sections 3 x 60° =180° • CE amplifier 180° • Total 180 + 180 = 360° LC oscillators: • A single LC section provides 180° • CE amplifier provides 180 ° • Total 360 ° 15.15 Crystal oscillator: • A quartz crystal with the desired value of the resonant frequency forms the frequencyselective feedback network • More accuracy and stability AC equivalent circuit of Quartz crystal: crystal AC equivalent circuit Resonant frequencies: • Series resonant frequency: 1 fs = -------------------2 Π LCS • Parallel resonant frequency: 1 fp = -------------------2 Π LCp Where Cp = (CM x CS) / (CM + CS) in the above figure Crystal controlled Colpitt oscillator: Resonant / tank circuit Crystal in feedback path to control frequency Crystal based Colpitt oscillator: Resonant / tank circuit Crystal in resonant / tank track to decide frequency 12.16 Voltage controlled oscillator (VCO): • A VCO is an oscillator circuit in which the frequency can be varied by an applied voltage • This is achieved by “varicap”, whose capacitance varies with applied voltage. • Varicap is used in tank circuit, which determines frequency Voltage-controlled Hartley oscillator: •Varicap used as voltage controlled capacitance in resonant / tank circuit •FET used as common-drain amplifier (Av little < 1) •Feedback factor β is large •To avoid noise effect 2 varicaps are used •Fine tuning the frequency is easy with VCO Feedback path 12.17 Frequency stability: • Oscillators ability to maintain constant frequency, for as long a period as possible • Frequency depends on: (large set of elements) – Circuit components – Stray elements (inter-electrode reactance) – Supply voltages – Active device’s characteristics • But largely frequency depends on RC or LC values (small set of elements) Frequency stability criterion: θ=phase-shift Ω=2Πf=frequency • A small set of elements (RC / RL) introduces a large change of phase-shift dθ for a given change in frequency dω, then higher the value of dθ ------, dω more will be the dependence on the these (RC / RL) circuit features • When dθ -----dω approaches infinity, ω is independent of other circuit features (large set of elements) • More the above ratio more the stability 13.1 Basic RC low pass circuit: Xc = R 1 XC = ----------------2Πf C Step & pulse response of LP circuit: 13.2 RC low pass circuit as integrator: Basics / fundas: 1. C=Q / V C= dq / dv ---- in integral form 2. I=Q / T i = dq / dt from 1 dv = dq / C from 2 = (1/C) i dt 1 v = ---- ∫ i dt C Numerical: 13.3 Basic RC high pass circuit: 13.4 RC high pass circuit as differentiator: 13.5 Basic RL circuit as integrator: 13.5 Basic RL circuit as differentiator: 13.9 Multivibrators: Multivibrator is a non-sinusoidal oscillator circuit with regenerative feedback with pulsed waveform. Types: 1. Bistable 2. Monostable 3. Astable Chapter 11: Oscillators The 555 Timer: 555 is a IC (integrated circuit) that is used to generate – 1. Accurate time delay (from µS to hours) – Monostable Operation (one stable state) 2. Rectangular signal – Astable Operation (no stable states) Both are non-stable states Non-stable state Stable state Here triggered This is Pulse Waveform Need not be triggered This is Rectangular Waveform Note: 1. Stable state = does not change, unless triggered. 2. Non-stable state = change state after fixed (designed) time. Chapter 11: Oscillators The 555 Timer: Refer next slide for SR FF Functional Block Diagram: