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The common collector amplifier's low output impedance allows a source with a large output impedance to drive a small load impedance without changing its voltage. Thus this circuit finds applications as a voltage buffer. In other words, the circuit has current gain (which depends largely on the h FE of the transistor) instead of voltage gain. A ...
This deleterious positive feedback results in thermal runaway. [2] There are several approaches to mitigate bipolar transistor thermal runaway. For example, Negative feedback can be built into the biasing circuit so that increased collector current leads to decreased base current. Hence, the increasing collector current throttles its source.
Paul Voigt patented a negative feedback amplifier in January 1924, though his theory lacked detail. [4] Harold Stephen Black independently invented the negative-feedback amplifier while he was a passenger on the Lackawanna Ferry (from Hoboken Terminal to Manhattan) on his way to work at Bell Laboratories (located in Manhattan instead of New Jersey in 1927) on August 2, 1927 [5] (US Patent ...
In this circuit, the base terminal of the transistor serves as the input, the collector is the output, and the emitter is common to both (for example, it may be tied to ground reference or a power supply rail), hence its name. The analogous FET circuit is the common-source amplifier, and the analogous tube circuit is the common-cathode amplifier.
In a typical Class A voltage amplifier, and class A and AB 1 power stages of audio power amplifiers, the DC bias voltage is negative relative to the cathode potential. The instantaneous grid voltage (sum of DC bias and AC input signal) does not reach the point where grid current begins.
Designers of purely solid-state class AB amplifiers with global negative feedback claimed closed-loop THD of no more than 0.003% throughout the audio range. [16] Lowest distortion buffer amplifiers employ a combination of a voltage operational amplifier and an off-the-shelf diamond buffer IC, enclosed in a common negative feedback loop. [12]
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Like a standard operational amplifier, the OTA also has a high impedance differential input stage and may be used with negative feedback. [3] But the OTA differs in that: The OTA outputs a current while a standard operational amplifier outputs a voltage. The OTA is usually used "open-loop"; without negative feedback in linear applications.