Bipolar transistor amplifier

The invention of the germanium transistor in 1947 [I, 2] marked the birth of modem microelectronics, a revolution that has profoundly influenced our current way of life. This early device was actually a bipolar transistor, a structure that is mainly used nowadays in amplifiers. However, logical circuits, and particularly microprocessors, preferentially use field-effect transistors (FETs), the concept of which was first proposed by Lilicnficld in 1930 [3], but was not used as a practical application until 1960 [4]. In a FET, the current flowing between two electrodes is controlled by the voltage applied to a third electrode. This operating mode recalls that of the vacuum triode, which was the building block of earlier radio and TV sets, and of the first electronic computers. 

A bipolar transistor may be used as a switch (either fully on with maximum current, or fully off with no current) and as an amplifier (always partly on). Bipolar transistors are the quickest devices. However the current flow through the base creates heat. This disadvantage makes bipolar transistors less popular than other devices such as metal oxide semiconductor transistor. 

High signal-to-noise ratios thus require the use of very low noise amplifiers and the limitation of bandwidth. The current technology offers differential amplifiers with voltage noise of less than 10 nV/VHz and current noise less than 1 pA/VHz. Both parameters are frequency dependent and decrease approximately with the square root of frequency. The exact relationship depends on the technology of the amplifier input stage. Field effect transistor (FET) preamplifiers exhibit about 5 times the voltage noise density compared to bipolar transistors but a current noise density that is about 100 times smaller. 

When an np rectifier is connected, through a shared p region, to a pn rectifier, we have a npn junction "triode" transistor, or bipolar junction transistor (BJT). This transistor can amplify signals, just as does the vacuum-tube triode, but by a totally different mechanism. 

Typical specifications of several common operational ampAAers are provided in Table 1. The LM741 BJT amplifier consists of 20 transistors incorporated in a single chip, which is produced in high volume at a cost of less than 1.00. The 741 was the Arst general-purpose op amp and is still used since it is inexpensive, robust, and adequate for many routine applications at frequencies below about 10 kHz. However, more recent bipolar versions offer improved specifications e.g., the LMll op amp has a much lower input bias current, which is important in minimizing errors in many op amp applications. 

Operational amplifiers that contain both bipolar and MOS or FET transistors on the same chip are termed BiMOS or BiFET op amps. These families have much higher input resistances ( 10 versus 10 fl for BJT op amps) and a frequency response generally... 

Currently, three basic high-frequency power amplifiers are in use the parallel connection of a bank of bipolar power transistors, the hybrid connection of parallel bipolar power transistors cascaded with metal oxide silicon field effect transistors (MOSFETs), and the bridge connection of MOSFETs. Each has unique properties and represents a stage in the evolution of ESUs. 

Transistors as the basic and crucial component for electronic circuits have been vigorously studied since 1947. The essential function of a transistor comes from its ability to control a larger signal by an apphed small signal between one pair of its terminals. This property makes the transistor as an amplifier or switch. According to the mechanism of the generation of carriers in the channel, transistors can be divided into three categories bipolar junction transistor, field-effect transistor, and electrochemical transistor. In electronic textile applications, the EET and ECT are employed to realize fibrous transistors. 

Central to electronics is the I-V measurement, that is, the measurement of the electrical current I through a device, as a function of the electrical potential, bias, or voltage V placed across it. Electrical devices can be (i) two-terminal devices (resistors, capacitors, inductors, rectifiers and vacuum-fube diodes, NDR devices), (ii) three-terminal devices (vacuum-tube triodes, bipolar junction transistors, or FETs), or, more rarely, (iii) four- or five-terminal devices (vacuum tetrodes, vacuum pentodes). Amplification is possible with two-terminal Esaki tunnel diodes and other NDR devices ( diode logic ), but most amplifying devices use fhree terminals. 

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