Transistor

The transistor is a solid state semiconductor device which can be used for amplification, switching, voltage stabilization, signal modulation and many other functions. It acts as a variable valve which, based on its input voltage, controls the current drawn by it from a connected voltage supply.

Usage

In the early days of transistor circuit design, the bipolar junction transistor, or BJT, was the most commonly used transistor. Even after MOSFETs became available, the BJT remained the transistor of choice for digital and analog circuits because of their ease of manufacture and ruggedness. However, the MOSFET has several desirable properties for digital circuits, and since major advancements in digital circuits have pushed MOSFET design to state-of-the-art, MOSFETs are now commonly used for both analog and digital purposes.

Related Topics:
Bipolar junction transistor - MOSFET

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Use in audio amplifiers

From mobile phones to televisions, vast numbers of products include audio amplifiers. The first discrete transistor audio amplifiers barely supplied a few hundred milliwatts, but power and audio fidelity gradually increased as better transistors became available and amplifier architecture evolved (single-ended transformer coupled to push-pull transformer coupled to push-pull capacitor coupled to push-pull direct coupled).

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In all but the most esoteric applications, audio amplifier ICs have replaced discrete transistor designs. Initially these chips were temperamental and they too, could only deliver a few hundred milliwatts. Today, for around $10 U.S, a complete 50 Watt audio power amplifier can be made with a few external components and an LM3886http://www.national.com/ds/LM/LM3886.pdf IC for example.

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Controversy surrounds the audio distortion aspects of transistor audio amplifiers as compared to vacuum tube audio amplifiers. Some high fidelity (Hi-Fi) audio amplifiers still use vacuum tubes, with their enthusiasts claiming that the sound is superior to transistorized amplifiers.

Related Topics:
High fidelity - Hi-Fi - Amplifiers - Enthusiasts

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Some argue that the larger number of electrons flowing in a vacuum tube behave with greater statistical accuracy, although this ignores the fact that vacuum tubes generally have a high-impedance control terminal (grid), and that discrete transistor circuits (as opposed to integrated circuits) can also be designed to use large currents.

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Others detect a distinctive "warmth" to the sound. The "warmth" is actually distortion caused by the vacuum tubes, which some audiophiles find pleasing. This is "soft-saturation" which occurs when vacuum tubes are overdriven, causing poorly designed vacuum tube amplifiers to sound better than poorly designed transistor amplifiers. Tube amplifiers are also less prone to slew-rate limiting, which was a problem with early semiconductors and is still observed in low-cost transistor audio amplifiers.

Related Topics:
Overdriven - Slew-rate

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Above speculative opinion gives no correlation between characteristics or measurements and perceived sound quality. See Tubes vs. Transistors - Is There An Audible Difference? and Transistors vs. Tubes - Brief Feature Comparison.

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Use in guitar amplifiers

Vacuum tubes are also preferred in guitar amplifiers which are designed to be overdriven, because they have a different non-linear transfer characteristic than transistors, and create a different, more pleasing spectrum of harmonic distortion or "fuzz". Digital signal processing (DSP) can be used to achieve similar effects in the digital domain.

Related Topics:
Guitar amplifiers - Digital signal processing

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It is possible to mix transistors and vacuum tubes in the same circuit, to utilize the benefits of both devices while minimizing their disadvantages.

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Use in computers

The "first generation" of electronic computers used vacuum tubes, which were hot, bulky, fragile and required high maintenance. Transistorizing the electronic computer was key to computer miniaturization. The "second generation" of computers through the late 1950s and 1960s featured boards filled with individual transistors, and magnetic cores. Subsequently, transistors and other components and their necessary wiring were integrated into a single, mass-manufactured component: the integrated circuit. In modern digital electronics, single transistors are very rare. Recently, inroads have been made in digital signal processing (DSP). DSP is a technique that can (among other things) be used with A/D and D/A converters to allow a digital processor (along with a computer program) to manipulate analog signals.

Related Topics:
1950s - 1960s - Integrated circuit - Digital signal processing - A/D - D/A

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