The Butler oscillator is a crystal-controlled oscillator that uses the crystal near its series resonance point. They are used where a simple low-cost circuit is needed which can oscillate at high frquencies (>50MHz [1] ) by using overtones of a crystal, and also giving low low phase noise. [2]
It was described by Butler in 1946 as the earthed grid oscillator, a derivative of the Hartley oscillator. [3] It is also known as the bridged-T oscillator or the grounded-base oscillator. [4]
The classic Butler oscillator circuit is a two-stage circuit with two non-inverting stages, a grounded base stage and an emitter follower. [5] The crystal is inserted in series in the overall feedback path. [5]
The more common modern form of the circuit uses just the emitter follower stage. [1] [6] The circuit may be analysed by considering it as a equivalent AC circuit with three parts. The emitter follower forms an amplifier with no phase shift. The crystal and its loading capacitor then produce a phase lag network, followed by the LC network of the resonant tank circuit. This then produces a phase lead, which overall meets the Barkhausen criteria for self-oscillation. [1]
The Butler circuit is a free-running or tuned oscillator. If the crystal is replaced temporarily with a low value resistor, the circuit will still oscillate at approximately the design frequency of the tank circuit. This allows the circuit to be set-up and adjusted initially without the crystal, and also encourages the selection of the correct crystal harmonic. [6] To avoid the circuit oscillating at the strong resonance of the crystal's fundamental, a small inductor may be placed in parallel with the crystal. [1] [6]
Both the better-known Pierce and Colpitts oscillator circuits may be considered as derivatives of the Butler. [6] [lower-roman 1]
An electronic oscillator is an electronic circuit that produces a periodic, oscillating or alternating current (AC) signal, usually a sine wave, square wave or a triangle wave, powered by a direct current (DC) source. Oscillators are found in many electronic devices, such as radio receivers, television sets, radio and television broadcast transmitters, computers, computer peripherals, cellphones, radar, and many other devices.
A Tesla coil is an electrical resonant transformer circuit designed by inventor Nikola Tesla in 1891. It is used to produce high-voltage, low-current, high-frequency alternating-current electricity. Tesla experimented with a number of different configurations consisting of two, or sometimes three, coupled resonant electric circuits.
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Resonance is a phenomenon that occurs when an object or system is subjected to an external force or vibration that matches its natural frequency. When this happens, the object or system absorbs energy from the external force and starts vibrating with a larger amplitude. Resonance can occur in various systems, such as mechanical, electrical, or acoustic systems, and it is often desirable in certain applications, such as musical instruments or radio receivers. However, resonance can also be detrimental, leading to excessive vibrations or even structural failure in some cases.
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