The gain in an open loop of an amplifier is the gain obtained when no global feedback is used in the circuit. The increase of the open loop in some amplifiers can be extremely high. An ideal operating amplifier has an infinite open loop gain. Typically, an op-amp may have a maximum open loop gain of about 10 ^ {5}. The very high rise of the op-amp loop allows a wide range of reaction levels to be applied to achieve the desired performance.
In the theory of electronic systems and control, loop gain is the sum of the gain, expressed as a ratio or in decibels, around a feedback loop. Feedback loops are widely used in electronics in amplifiers and oscillators and, generally, in both electronic control electronics and electronic control systems to control industrial installations and equipment. The concept is also used in biology.
In a feedback loop, the output of a device, process or plant is sampled and applied to modify the input to better control the output. Loop gain, along with the related concept of loop phase change, determines the behavior of the device and especially whether the output is stable or unstable, which can lead to oscillation. The importance of loop gain as a parameter for characterizing electronic feedback amplifiers was first recognized by Heinrich Barkhausen in 1921 and was further developed by Hendrik Wade Bode and Harry Nyquist at Bell Labs in the 1930s.
The input signal is applied to the gain amplifier A in open and amplified loop. The output of the amplifier is applied to a gain network of β and is low from the input to the amplifier. The loop gain is calculated by imagining the feedback loop is broken at a certain point, and net gain calculation, if a signal is applied. Loop gain is the product of amplifier gains and feedback network, -Ab. The minus sign is due to the fact that the feedback signal is pulled out of the input.
The A and b gains and hence the loop gain generally vary with the input signal frequency and are usually expressed as roaming angle ω in radians per second. It is often displayed as a graph with the horizontal axis axis ω and the gain of the vertical axis. In amplifiers, loop gain is the difference between the open loop gain curve and the loop gain curve (in fact curve 1 / b) on a dB scale.
