He managed to develop stable negative feedback amplifiers in the 1930s.

This section describes the step response of a simple negative feedback amplifier shown in Figure 1.

However, a negative feedback amplifier can be unstable such that it may oscillate.

Thus, with the help of Nyquist's theory, he managed to demonstrate a stable negative feedback amplifier which can be used in reality.

A more general way to model negative feedback amplifiers including this effect is with the asymptotic gain model.

See the article on negative feedback amplifier and references by Meyer or Sedra.

Once the stability problem is solved, the negative feedback amplifier is extremely useful in the field of electronics.

A general expression for the gain of a negative feedback amplifier is the asymptotic gain model.

Harold Stephen Black invented the negative feedback amplifier.

Harold Stephen Black revolutionized the field of applied electronics by inventing the negative feedback amplifier in 1927.

The steps in deriving the gain using the asymptotic gain formula are outlined below for two negative feedback amplifiers.

The Negative feedback amplifier allowed Bell system to reduce overcrowding of lines and extend its long-distance network by means of carrier telephony.

Connecting a resistor between the output and the input biases the TTL element as a negative feedback amplifier.

A negative feedback amplifier has gain given by (see negative feedback amplifier):

The negative feedback amplifier was invented by Harold Stephen Black at Bell Laboratories in 1927, and patented by him in 1934.

The asymptotic gain model (also known as the Rosenstark method) is a representation of the gain of negative feedback amplifiers given by the asymptotic gain relation:

He held many patents the most famous of which was US Patent 2,102,671 "Wave Translation System", which was issued to Bell Laboratories in 1937, covering the negative feedback amplifier.

A negative feedback amplifier (or more commonly simply a feedback amplifier) is an amplifier which combines a fraction of the output with the input so that a negative feedback opposes the original signal.

A negative feedback amplifier, or more commonly simply a feedback amplifier, is an amplifier which uses negative feedback to improve performance and reduce sensitivity to parameter variations due to manufacturing or environmental uncertainties.

In modern control theory textbooks, the Cauchy argument principle is quite frequently used to derive the Nyquist stability criterion, which can be used to predict the stability of negative feedback amplifier and negative feedback control systems.

According to Black he got his inspiration to invent the negative feedback amplifier when he was traveling from New Jersey to New York City by taking a ferry to cross the Hudson River in August 1927.

After years of work Black invented the negative feedback amplifier which uses negative feedback to reduce the gain of a high-gain, non-linear amplifier and makes it act as a low-gain, linear amplifier with much lower noise and distortion.

It is essentially a negative feedback amplifier which was used in the Vox T60 pre amp, as well as also being used in the 6 channel Vox MKII & MKIII Mixer.

That is, the ideal current gain A is reduced not only by the loading factors, but due to the bilateral nature of the two-port by an additional factor ( 1 + β (R / R ) A ), which is typical of negative feedback amplifier circuits.