Wiktor Wise
In electrical engineering, electrical balance or a balanced circuit is electronic circuitry for use with a balanced line, or the balanced line itself. A balanced line is a line in which the two wires will carry balanced currents (that is, equal and opposite currents) when balanced (symmetrical) voltages are applied. The condition for the balance of lines and circuits is that the impedances are balanced. In telecommunications and professional audio, a balanced line or balanced signal pair is an electrical circuit consisting of two conductors of the same type, both of which have equal impedances along their lengths, to ground, and to other circuits. The term electrically balanced is also used in chemistry to refer to a chemical entity that is electrically neutral, with no excess or partial electrical charges.
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What You'll Learn
Electrical balance in the brain
Balance is essential for almost everything we do, from walking to cycling. It is, therefore, no surprise that electrical balance is key to understanding how our brains function. The brain sends and receives chemical and electrical signals throughout the body, controlling various processes.
In neural networks, excitation/inhibition (E/I) balance occurs when the average levels of excitatory signals match those of the inhibitory signals received from all connections. Neurons maintain this balance, and a loss of it is associated with serious problems such as epilepsy, schizophrenia, and autism. E/I balance is present in the whole brain and individual neurons.
The E/I balance and another phenomenon, the E/I delay, form the biophysical roots of 'normalization'. Normalization is the process by which our brains make sense of the world despite receiving a wide range of information.
Aanchal Bhatia and Sahil Moza, researchers at the National Centre for Biological Sciences (NCBS), Bangalore, conducted a study to investigate if E/I balance was maintained within a sub-circuit. They stimulated neurons in mouse brain slices with different patterns of light using a technique called optogenetics. The team focused on a specific circuit in the hippocampal region of the brain called the CA3-CA1 circuit, which is known for its role in memory formation. The researchers found that sub-circuits maintain a very precise E/I balance, even with random patterns of input.
The study provides valuable insights into how the brain computes. It highlights the ability of neurons to selectively pay attention to important signals by tweaking the balance.
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Balanced circuits and lines in electrical engineering
In electrical engineering, a balanced circuit is electronic circuitry for use with a balanced line, or the balanced line itself. A balanced line is a common method of transmitting various electrical signals between two points using two wires.
A balanced circuit will typically show a symmetry of its components about a horizontal line midway between the two conductors. This is different from a symmetrical circuit, which shows symmetry about a vertical line at its midpoint. While physical symmetry is not a requirement for a balanced circuit, electrical impedances must be symmetrical. A balanced signal is one where the voltages on each wire are symmetrical with respect to ground or another reference point. The two sides of a balanced circuit have identical transmission characteristics, and the two wires carry equal and opposite currents when symmetrical voltages are applied.
To maintain the balance, the circuit blocks interfacing with the line or connected in the line must also be balanced. This is achieved by ensuring that the impedances are balanced and that the circuit detects only differential signals, rejecting common-mode signals. The conceptually simplest way to connect to a balanced line is through transformers at each end. The transformers isolate the line from earth and earth loop currents. The side of the transformer facing the line will have the winding laid in two carefully balanced parts to maintain line balance.
Balanced lines are often used in conjunction with differential signalling, where signals have equal amplitudes but opposite polarities on each leg. However, this is not a requirement for a balanced line, and noise rejection in balanced cables does not depend on differential signalling. The primary advantage of balanced lines is the rejection of common-mode noise and interference when fed to a differential device. This is achieved through various methods, including twisting the conductors together to ensure that each conductor is exposed to the same external magnetic fields, electrostatic shielding, and the use of 4-conductor star quad cable.
Balanced circuits are commonly used in professional applications, particularly in live sound and studio settings where longer cable runs are required. Examples of their use include connections between microphones and mixers, XLR inputs on mixers, and connections between amplifiers and speakers.
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Apolar molecules in chemistry
In the context of electrical engineering, being electrically balanced refers to having a balanced circuit. A balanced circuit is an electronic circuit designed for use with a balanced line, which is a common method of transmitting electrical signals between two points on two wires.
Now, in chemistry, the concept of polarity is important in understanding the behaviour of molecules. A polar molecule is one that has a charge on one side that is not cancelled out, resulting in a region of partial charge. Specifically, one end of the molecule is slightly positive, while the other end is slightly negative. These charged regions are called poles, similar to the north and south poles of a magnet. A molecule with two poles is called a dipole.
Apolar molecules, also known as non-polar molecules, are those that do not have a charge separation. In other words, they have equal charges on both ends. This occurs when the electronegativities of the atoms within the molecule are identical, resulting in a difference of zero. Another way for a molecule to be non-polar is if it has polar bonds that are arranged symmetrically, such as in carbon dioxide (CO2) or carbon tetrachloride. In these cases, the individual dipoles cancel each other out due to their symmetrical arrangement, resulting in an overall molecular polarity of zero.
The distinction between polar and apolar molecules is crucial in chemistry because it influences various physical properties of substances. For example, polar molecules tend to have higher boiling points than non-polar molecules of similar molar mass due to stronger intermolecular attractions. Additionally, polar compounds generally have higher surface tension and solubility in water, while most non-polar compounds are water-insoluble (hydrophobic) at room temperature.
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Differential signalling
The technique of differential signalling minimises electronic crosstalk and electromagnetic interference, both noise emission and acceptance. It can achieve a constant or known characteristic impedance, allowing for impedance matching techniques important in high-speed signal transmission lines or high-quality balanced line and balanced circuit audio signal paths. Differential pairs generally carry differential or semi-differential signals, such as high-speed digital serial interfaces. Differential signalling is often used in computers to reduce electromagnetic interference, as complete screening is not possible with microstrips and chips due to geometric constraints.
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Noise rejection in balanced cables
In electrical engineering, a balanced circuit is electronic circuitry for use with a balanced line, or the balanced line itself. A balanced line is a common method of transmitting electrical signals between two points on two wires.
A balanced line or balanced signal pair consists of two conductors of the same type, with equal impedances along their lengths, to ground, and to other circuits. The two signal lines have matched impedances to ensure that any interference induced in the line is common-mode and can be removed at the receiving end by circuitry with good common-mode rejection.
The noise rejection in balanced cables works because the interfering noise from the surrounding environment induces equal noise voltages into both wires. This is due to the close physical proximity of the wires, which ensures that any EM interference is almost identical on both wires. The noise is then filtered out by measuring the voltage difference between the two wires at the receiving end, allowing the original signal to be recovered while the noise is rejected.
The balanced nature of the circuit allows for "COMMON MODE REJECTION", where the hot signal has the signal plus the noise, and the cold signal has just the noise. Inside the gear, the noise from the cold signal is reversed in phase, creating the inverse phase of the noise on the hot signal. This results in a zero amplitude noise, as +1 and -1 sum to 0, leaving only the original intended signal.
Additionally, some balanced lines have electrostatic shielding, such as foil, copper wire, or a copper braid, to further enhance noise rejection by reducing the amount of noise introduced. This shield provides immunity to RF interference but is ineffective against magnetic fields. To address this, some balanced lines use 4-conductor star quad cables to provide immunity to magnetic fields. The geometry of the cable ensures that magnetic fields cause equal interference in both legs of the balanced circuit, creating a common-mode signal that can be easily removed by a transformer or balanced differential receiver.
Overall, the noise rejection capabilities of balanced cables make them advantageous for transmitting electrical signals with minimal interference, particularly in applications such as sound recording and reproduction, where they are commonly referred to as balanced audio.
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Frequently asked questions
In electrical engineering, electrical balance or a balanced circuit refers to electronic circuitry for use with a balanced line. A balanced line is a common method of transmitting electrical signals between two points on two wires. The two signal lines are of matched impedance to ensure that any interference induced in the line is common-mode and can be removed at the receiving end.
A balanced signal is one where the voltages on each wire are symmetrical with respect to ground or another reference point. This means that the signals are inverted with respect to each other.
Balanced lines are used in telecommunications and professional audio to transmit signals between two points. They are effective at rejecting common-mode noise and interference when fed to a differential device such as a transformer or differential amplifier.
In chemistry, the term "electrically balanced" is used to describe a chemical entity that is apolar or non-polar, meaning it has no electrical poles and no excess or partial electrical charges.
