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A gain greater than one (greater than zero dB), that is, amplification, is the defining property of an active device or circuit, while a passive circuit will have a gain of less than one. [ 4 ] The term gain alone is ambiguous, and can refer to the ratio of output to input voltage ( voltage gain ), current ( current gain ) or electric power ...
First-order RC filter low-pass filter circuit. Roll-off of a first-order low-pass filter is 20 dB/decade (≈6 dB/octave) A simple first-order network such as a RC circuit will have a roll-off of 20 dB/decade. This is a little over 6 dB/octave and is the more usual description given for this roll-off.
The decibel originates from methods used to quantify signal loss in telegraph and telephone circuits. Until the mid-1920s, the unit for loss was miles of standard cable (MSC). 1 MSC corresponded to the loss of power over one mile (approximately 1.6 km) of standard telephone cable at a frequency of 5000 radians per second (795.8 Hz), and matched closely the smallest attenuation detectable to a ...
For example: an amplifier with a PSRR of 100 dB in a circuit to give 40 dB closed-loop gain would allow about 1 millivolt of power supply ripple to be superimposed on the output for every 1 volt of ripple in the supply. This is because = .
For these amplifiers, the 1 dB compression point is defined as the input power (or output power) where the gain is 1 dB less than the small signal gain. Sometimes this non linearity is deliberately designed in to reduce the audible unpleasantness of hard clipping under overload. Ill effects of non-linearity can be reduced with negative feedback.
Typically an op-amp may have a maximal open-loop gain of around , or 100 dB. An op-amp with a large open-loop gain offers high precision when used as an inverting amplifier. Normally, negative feedback is applied around an amplifier with high open-loop gain, to reduce the gain of the complete circuit to a desired value.
A measure of the power contained in the useful part of the signal, to the power contained in noise. Often measured in decibels; for example, in sound reproduction a 40 or 50 decibel signal to noise ratio would be broadcast quality, whereas a 10 decibel ratio would represent very difficult operating conditions for a voice radio system.
This is more commonly used than scalar linear gain and a positive quantity is normally understood as simply a "gain", while a negative quantity is a "negative gain" (a "loss"), equivalent to its magnitude in dB. For example, at 100 MHz, a 10 m length of cable may have a gain of −1 dB, equal to a loss of 1 dB.