Phase-shift oscillator

Phase-shift oscillator

A phase-shift oscillator is a simple sine wave electronic oscillator. It contains an inverting amplifier, and a feedback filter which 'shifts' the phase by 180 degrees at the oscillation frequency.

The filter must be designed so that at frequencies above and below the oscillation frequency the signal is shifted by either more or less than 180 degrees. This results in constructive superposition for signals at the oscillation frequencies, and destructive superposition for all other frequencies.

The most common way of achieving this kind of filter is using three cascaded resistor-capacitor filters, which produce no phase shift at one end of the frequency scale, and a phase shift of 270 degrees at the other end. At the oscillation frequency each filter produces a phase shift of 60 degrees and the whole filter circuit produces a phase shift of 180 degrees.

Op-Amp implementation

One of the simplest implementations for this type of oscillator uses an operational amplifier (op-amp), three capacitors and four resistors, as shown in the diagram.

The mathematics for calculating the oscillation frequency and oscillation criterion for this circuit are surprisingly complex, due to each R-C stage loading the previous ones. The calculations are greatly simplified by setting all the resistors (except the negative feedback resistor) and all the capacitors to the same values.In the diagram, if R1 = R2 = R3 = "R", and C1 = C2 = C3 = "C", then:

f_{Oscillation}=frac{1}{2pi RCsqrt{6

and the oscillation criterion is:

R_{feedback}=29cdot R

Without the simplification of all the resistors and capacitors having the same value, the calculations become more complex:

f_{Oscillation}=frac{1}{2pisqrt{R_2R_3(C_1C_2+C_1C_3+C_2C_3)+R_1R_3(C_1C_2+C_1C_3)+R_1R_2C_1C_2

Oscillation criterion:R_{feedback}= 2(R_1+R_2+R_3)+frac{2R_1R_3}{R_2}+frac{C_2R_2+C_2R_3+C_3R_3}{C_1}+frac{2C_1R_1+C_1R_2+C_3R_3}{C_2}+frac{2C_1R_1+2C_2R_1+C_1R_2+C_2R_2+C_2R_3}{C_3}+frac{C_1R_1^2+C_3R_1R_3}{C_2R_2}+frac{C_2R_1R_3+C_1R_1^2}{C_3R_2}+frac{C_1R_1^2+C_1R_1R_2+C_2R_1R_2}{C_3R_3}

Another version of this circuit can be made by putting an op-amp buffer between each R-C stage which simplifies the calculations.


Wikimedia Foundation. 2010.

Игры ⚽ Поможем написать реферат

Look at other dictionaries:

  • Phase-locked loop — PLL redirects here. For other uses, see PLL (disambiguation). A phase locked loop or phase lock loop (PLL) is a control system that generates an output signal whose phase is related to the phase of an input reference signal. It is an electronic… …   Wikipedia

  • Delay line oscillator — A delay line oscillator is a form of electronic oscillator that uses a delay line as its principal timing element. The circuit is set to oscillate by inverting the output of the delay line and feeding that signal back to the input of the delay… …   Wikipedia

  • Electronic oscillator — An electronic oscillator is an electronic circuit that produces a repetitive electronic signal, often a sine wave or a square wave.A low frequency oscillator (LFO) is an electronic oscillator that generates an AC waveform between 0.1 Hz and 10 Hz …   Wikipedia

  • RC oscillator — Electronic oscillators are often designed around an LC tank circuit, a tuned circuit formed with an inductor and a capacitor. But use of an inductor is not a requirement. Instead, the tuned circuit can be built using just resistors and capacitors …   Wikipedia

  • phase-lock — v. [trans.] Electronics fix the frequency of (an oscillator or a laser) relative to a stable oscillator of lower frequency by a method that utilizes a correction signal derived from the phase difference generated by any shift in the frequency …   Useful english dictionary

  • Pierce oscillator — The Pierce oscillator is a type of electronic oscillator circuit particularly well suited for implementing crystal oscillator circuits. Named for its inventor, George W. Pierce (1872 1956), the Pierce oscillator is a derivative of the Colpitts… …   Wikipedia

  • Frequency Shift Keying — Bildung eines binären FSK Signals. Oben: Quelldaten als eine Folge von logisch 1 und logisch 0. Mitte: Unmodulierte Trägerfrequenz Unten: Moduliertes FSK Signal. Die Frequenzumtastung (englisch Frequency Shift Keying, FSK) ist eine… …   Deutsch Wikipedia

  • Frequenz-Shift-Keying — Bildung eines binären FSK Signals. Oben: Quelldaten als eine Folge von logisch 1 und logisch 0. Mitte: Unmodulierte Trägerfrequenz Unten: Moduliertes FSK Signal. Die Frequenzumtastung (englisch Frequency Shift Keying, FSK) ist eine… …   Deutsch Wikipedia

  • Minimum Shift Keying — Bildung eines binären FSK Signals. Oben: Quelldaten als eine Folge von logisch 1 und logisch 0. Mitte: Unmodulierte Trägerfrequenz Unten: Moduliertes FSK Signal. Die Frequenzumtastung (englisch Frequency Shift Keying, FSK) ist eine… …   Deutsch Wikipedia

  • Backward wave oscillator — A backward wave oscillator (BWO), also called carcinotron (a trade name for tubes manufactured by CSF, now Thales) or backward wave tube, is a vacuum tube that is used to generate microwaves up to the terahertz range. It belongs to the traveling… …   Wikipedia

Share the article and excerpts

Direct link
… Do a right-click on the link above
and select “Copy Link”