A bridge oscillator generates sine waves and is often used as an audio frequency oscillator due to its low distortion and ease of tuning. It is based on a bridge circuit with four resistors and two capacitors. The design was first described by William Hewlett in his master’s thesis and later used in HP’s first product. The oscillator’s low distortion is achieved through the use of a thermistor, such as an incandescent light bulb, to stabilize amplitude. Light bulbs have since been replaced with less sensitive thermistors.
A bridge oscillator is an electronic oscillator that generates a wide range of frequencies in the form of sine waves. Oscillators are circuits that produce repetitive electronic signals. They are often used to transmit television or radio signals or produce sound for an electronic device. The sounds produced by an oscillator cannot be heard on their own, but must be converted into audible sound through the use of speakers or other devices. The bridge oscillator is often used as an audio frequency oscillator because it is easy to tune and has low distortion.
The word bridge refers to the structure of the circuit used. A bridge circuit is an electrical circuit in which two circuit branches are bridged or crossed by a third. A branch circuit is any electrical circuit divided into two or more parallel circuits. This results in each circuit getting half the current coming from the main line. The bridge consists of four resistors and two capacitors.
The bridge oscillator circuit structure is based on a network developed by German physicist Max Wein in 1891. Accordingly, a bridge oscillator is sometimes referred to as a Wein bridge oscillator, even though Wien did not actually create one. The technology needed for the oscillators didn’t exist until decades after Wein created the circuit for him.
The credit for creating the bridge oscillator actually goes to William Hewlett. He first described this type of oscillator in his master’s thesis he wrote for Standford University in 1939. That same year, Hewlett founded the information technology company Hewlett-Packard (HP) with David Packard. Hewlett and Packard used the technology described in his thesis to create HP’s first product, the HP2001A. Hewlett was granted a patent for the bridge oscillator design in January 1942.
One of the main advantages of this type of oscillator is its low distortion. This is only possible because the amplitude, or magnitude of the change created is well established. Hewlett achieved this stabilization by using an incandescent light bulb as the thermistor.
A thermistor is a resistor that varies its resistance depending on the temperature. The resistance of a light bulb increases as the temperature rises. A light bulb is therefore a positive temperature coefficient thermistor. Since Hewlett’s first bridge oscillator, light bulbs have been replaced with diodes or other types of thermistors that are less sensitive to vibration.
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