Home > 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. Such an oscillator is referred to as an RC oscillator.1 Sine Wave Oscillators
Two configurations are common. One is called a Wien Bridge (also called a "Wein Bridge"; there appears to be some disagreement about the correct spelling). In this circuit, two RC circuits are used, one with the RC components in series and one with the RC components in parallel. The Wien Bridge is often used in audio signal generators because it can be easily tuned using a two-section variable capacitor. The architypical HP 200 audio oscillator is a Wien Bridge oscillator.
The second common design is called a "Twin-T" oscillator as it uses two "T" RC circuits operated in parallel. One circuit is an R-C-R "T" which acts as a low-pass filter. The second circuit is a C-R-C "T" which operates as a high-pass filter. Together, these circuits form a bridge which is tuned at the desired frequency of oscillation.
If they are to produce an undistorted sine wave, RC oscillators usually require some form of amplitude control. Many common designs simply use an incandescent lamp in the feedback circuit. These oscillators take advantage of the fact that the resistance of the tungsten filament increases in proportion to its temperature. Operated well below the point at which the filament actually illuminates, the increasing resistance reduces the feedback signal, limiting the oscillator's signal to the linear range. (That is, clippingClipping has several meanings: Telecommunications In telecommunication, the term clipping has the following meanings: #In telephony, the loss of the initial or final parts of a word, words, or syllable, usually caused by the nonideal operation of voice-ac is prevented.) The 200 oscillator used this technique.
More-sophisticated oscillators measure the output level and use this as feedbackIn cybernetics and control theory, feedback is a process whereby some proportion or in general, function, of the output signal of a system is passed (fed back) to the input. Often this is done intentionally, in order to control the dynamic behaviour of th to control the gain of the amplifierAn amplifier is a device which changes a small movement into a larger movement. The relationship of the input to the output--usually expressed as a function of the input frequency--is called the transfer function of the amplifier, and the magnitude of the within the oscillator.
2 Non-Sine Wave Oscillators
Many designs exist for RC oscillators that are not required to produce a sine wave. MultivibratorA multivibrator is an electronic circuit used to implement a variety of simple two-state systems such as oscillators, timers and flip-flops. The commonest form is the astable or oscillating type, which generates a square wave the high level of harmonics is are one approach. The 555 timer ICThe 555 is a integrated circuit (chip) implementing a variety of timer and multivibrator applications. Introduced in 1971 by Signetics (later acquired by Philips), it is still in wide use, thanks to its ease of use, low price and good stability. The purpo is another very common approach. Most non-sine wave RC oscillators require only a single RC network.
Electrical circuits
