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Electronics2 - vili.pmmf.huvili.pmmf.hu/~fuzi/Electronics2/Ex2Lt07.pdf · Meissner oscillator...

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Electronics 2 Lecture 7 Sine-wave generators Literature - U. Tiecze, Ch. Schenk: Analogue and digital electronic circuits - B Carter, TR Brown: Handbook of Operational Amplifier Applications, TI, 2001 - Ron Mancini (ed): Op Amps for Everyone, Texas Instruments, 2002
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Electronics 2

Lecture 7

Sine-wave generators

Literature- U. Tiecze, Ch. Schenk: Analogue and digital electronic circuits- B Carter, TR Brown: Handbook of Operational Amplifier Applications, TI, 2001- Ron Mancini (ed): Op Amps for Everyone, Texas Instruments, 2002

Oscillator principle of operation

Oscillator circuit

Amplitude condition:

Phase condition (positive feedback):

LC oscillator

General oscillation condition:

Open loop gain:

Oscillators with operational amplifiers

Autonomous oscillations emerge when the denominator is 0.

The large gain of the op amps ensures oscillation (component noise is sufficient to provide output signal). Available frequency: several kHz (at higher frequencies the phase lag of the op amp is too large). Current feedback op amps have significantly larger bandwidth, but are sensitive to capacitive feedback.

General complex oscillation condition:

Amplitude condition:

Phase condition (negative feedback):

Typical oscillator characteristics

Meissner oscillator

Alexander Meißner, 1913Feedback with transformer in the collector circuit.

Tuned collector circuit, common base implementation

Tuned collector circuit, common emitter implementation

Armstrong oscillator

Edwin Howard Armstrong, 1914

Tuning in the gate circuit

Hartley oscillator

Ralph Hartley, 1915

inductive three-point oscillator

With FET amplifier

With common emitter bipolar transistor

k: magnetic coupling coefficient

Colpitts oscillator

Edwin Henry Colpitts, 1919

capacitive three-point oscillator

Common emitter Common base Emitter coupled push-pull

Clapp oscillator

James Kilton Clapp, 1948

C1, C2: voltage divider, determines the measure of positive feedback;C0: tuning capacitor to adjust the frequency.

Vackár oscillator

Jiri Vackár, 1949

L1, Ca and C0: the resonant circuit of the Colpitts oscillator, C0 is the tuning capacitor. Cg and Cv: gate voltage divider.

Can be tuned in a wider frequency range than the Colpitts or Clapp oscillators.

Wien bridge oscillators

Av 3 Lin = R2C

William Reddington Hewlett, 1939

= − R

HP200A – the first Hewlett-Packard product: precision sinewave generator

Wien bridge oscillators

Wien – Robinson oscillator

Wien – Robinson bridge

Accurate values R1 larger by 5%

Wien bridge oscillators

Wien – Robinson oscillator

Wien-bridge oscillator with gain control

Regulating resistor with negative temperature coefficient

Regulating resistor with positive temperature coefficient

A =3

Wien-bridge oscillator with diode gain control

Cutting the peaks causes significant distortion.

Tunable Wien-bridge oscillator with FET gain control

The channel resistance of the FET increases with the current amplitude.

Double T filter oscillator

More difficult to tune than the Wien bridge oscillators, but works with lower distortion.

Double T is a stopband filter. Cancels the negative feedback at resonance frequency.

Bridged T oscillator

Bridged T is a stopband filter.

At resonance the gain is 2/3.

Push-pull oscillators

With inductive coupling With capacitive coupling

Used at high powers, exploit the higher efficiency of B class amplifiers.

Relaxation oscillators

Pearson-Anson oscillator

When the voltage on the capacitor reaches the ignition value the neon lamp flashes, the capacitor is discharged and the charging process starts again.

Hysteresis-oscillator

Quartz crystal oscillator

Tuning with capacitor in series connection:

Series resonance frequency

Equivalent scheme of a quartz crystal:

Typical parameters of a 4MHz quartz:

Parallel resonance frequency:

Quartz crystal oscillator

George W. Pierce, 1923

Common emitter stage With CMOS inverter Emitter-coupled multivibrator

Quartz stabilized oscillators

Hartley Colpitts Emitter-coupled

Phase shift oscillator

Four stage case:

A =29

A =18.36

Three-phase phase shift oscillator

Every unit provides 120° phase shift.

Phase shift Bubba oscillator

A =4

Sine wave signals with 45° phase lag emerge at the amplifier output terminals.


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