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Both types of BJT function by letting a small current input to the base control an amplified output from the collector. The result is that the BJT makes a good switch that is controlled by its base input. The BJT also makes a good amplifier, since it can multiply a weak input signal to about 100 times its original strength.
Common-emitter amplifiers give the amplifier an inverted output and can have a very high gain that may vary widely from one transistor to the next. The gain is a strong function of both temperature and bias current, and so the actual gain is somewhat unpredictable.
Figure 1: Basic NPN common collector circuit (neglecting biasing details).. In electronics, a common collector amplifier (also known as an emitter follower) is one of three basic single-stage bipolar junction transistor (BJT) amplifier topologies, typically used as a voltage buffer.
Figure 1: Basic NPN common base circuit (neglecting biasing details). In electronics, a common-base (also known as grounded-base) amplifier is one of three basic single-stage bipolar junction transistor (BJT) amplifier topologies, typically used as a current buffer or voltage amplifier.
Various configurations of single transistor amplifiers are possible, with some providing current gain, some voltage gain, and some both. From mobile phones to televisions, vast numbers of products include amplifiers for sound reproduction, radio transmission, and signal processing. The first discrete-transistor audio amplifiers barely supplied ...
Fig. 4 Top: Small-signal BJT cascode using hybrid-pi model Bottom: Equivalent circuit for BJT cascode using amplifier low-frequency parameters. The g-parameters found in the above formulas can be used to construct a small-signal voltage amplifier with the same gain, input and output resistance as the original cascode (an equivalent circuit).
It is commonly used in modern ultrafast circuits, mostly radio frequency (RF) systems, and in applications requiring a high power efficiency, such as RF power amplifiers in cellular phones. The idea of employing a heterojunction is as old as the conventional BJT, dating back to a patent from 1951. [1]
The junction version known as the bipolar junction transistor (BJT), invented by Shockley in 1948. [10] Later the similar thyristor was proposed by William Shockley in 1950 and developed in 1956 by power engineers at General Electric (GE). The metal–oxide–semiconductor field-effect transistor (MOSFET) was also invented at Bell Labs.