Molly Ayala
In electronics, 'noise' refers to unwanted high-frequency disturbances or interference in a circuit. This noise can be caused by various factors, including electromagnetic interference, voltage fluctuations, current variations, and external environmental factors such as lightning discharges or electrical equipment. Noise can also be generated within the circuit itself due to thermal effects or signal processing techniques like dithering. The impact of noise can range from minor audio distortions to significant disruptions in sensitive electronic equipment. Understanding and mitigating noise in electrical circuits is crucial for maintaining the proper functioning and accuracy of electronic devices and systems.
| Characteristics | Values |
|---|---|
| Definition | Noise refers to variations in voltage or current that are often random, usually of relatively low amplitude, and always undesirable. |
| Types | Thermal noise, burst noise, flicker noise, shot noise, electrostatic noise, magnetic-coupled noise, inductive coupling, capacitive coupling, conducted noise, cosmic noise, solar noise, industrial noise, static noise, etc. |
| Causes | Resistance to the flow of electrons, lightning discharges, electrical disturbances in nature, solar storms, distant stars, industrial sources like automobiles, aircraft, ignition electric motors, etc. |
| Impact | Unwanted interference or disturbance in the circuit, voltage sags, transient waveforms, etc. |
| Solutions | Faraday cage, improved circuit layout and grounding, notch filters, twisted pair wiring, cooling of circuits, smaller resistors, filters to limit bandwidth, low-current biasing techniques, transient protection, etc. |
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What You'll Learn
Sources of electrical noise
Noise in electrical circuits can come from anywhere, be it the air, the power supply, an LDO, a switching regulator, or a resistor. It is caused by random electrical signals that interfere with the desired signal, resulting in degraded circuit and system performance. Noise can be classified into two categories: intrinsic and extrinsic.
Intrinsic noise sources are inherent to the electronic devices in question and arise from fundamental physical effects. Examples of intrinsic noise include thermal (or Johnson) noise, which is related to temperature, resistance, and bandwidth; electronic shot noise; and 1/f noise. Higher temperatures and higher resistance lead to higher noise amplitude.
Extrinsic noise sources arise outside the circuit or from interactions with the surrounding environment. External sources of noise include power lines, RF transmitters, nearby conductors, ignition systems, or motors that turn on and off, drawing sudden large currents. Electromagnetic interference (EMI) is a type of external noise caused by current in nearby conductors or cables. Radio frequency interference (RFI) is another source of external noise caused by radiating signals from wireless systems.
Noise can also be transmitted through power cords acting as antennas or carried through power lines. These disturbances can be generated by radio frequency interference, such as radio, TV, cellular, and microwave transmissions, radar, arc welding, and distant lightning. Additionally, electromagnetic interference produced by heaters, air conditioners, white goods, and other thermostat-controlled or motor-operated devices can contribute to noise.
In an office setting, a laser copier/printer can be a significant source of noise due to the constant switching of its internal heater, causing voltage sags and generating transients that can affect other equipment on the same branch circuit.
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Types of electrical noise
Noise in an electrical circuit refers to random and unpredictable variations in voltage or current that are undesirable. This noise can interfere with the quality and performance of electronic circuits and can originate from internal or external sources. The two main categories of noise are intrinsic and extrinsic.
Intrinsic Noise
Intrinsic noise, also known as internal noise, is inherent to the physical components and processes of the circuit. Some common types of intrinsic noise include:
- Thermal noise: This is caused by the random thermal motion of electrons and holes inside a conductor due to resistance. Higher temperatures and higher resistance lead to higher noise amplitude.
- Shot noise: Shot noise is caused by the random arrival of electrons and holes at the output element or collector in a transistor or across a PN junction. It occurs due to discontinuities in the device, such as the contact between a copper lead and a semiconductor material.
- Flicker noise: Also known as 1/f noise, it occurs in almost all electronic devices and results from various effects. It is characterised by a frequency spectrum that falls off steadily into higher frequencies, with a pink spectrum.
- Burst noise: This occurs only in semiconductors and is caused by imperfections in the semiconductor material, leading to abrupt voltage or current transitions. It produces a popping or crackling sound in audio circuits, resembling popcorn popping.
- Transit noise: This internal noise is caused by the energy transfer between electrons and ions as they travel from the emitter to the collector of a transistor. It is more prominent at higher frequencies when the transit time becomes comparable to the period of the signal being amplified.
Extrinsic Noise
Extrinsic noise, or external noise, comes from sources outside the circuit. Some common types of extrinsic noise include:
- Electromagnetic interference: This is a common type of noise caused by electromagnetic fields interacting with the circuit.
- Power supply noise: It is caused by fluctuations in the power supply, such as voltage surges or AC ripple in the DC power supply output.
- Atmospheric noise: Naturally occurring disturbances in the Earth's atmosphere, such as lightning discharges during thunderstorms, contribute to atmospheric noise.
- Industrial noise: This type of noise is produced by various man-made sources, including automobiles, aircraft, electric motors, high-voltage switchgear, and fluorescent lamps.
- Cosmic noise: Distant stars generate noise, and while individual stars have minimal impact, their collective effect is significant in the frequency range of about 20 to 120 MHz.
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Reducing electrical noise
Electrical noise is a generic term for undesired variations in voltage or current that are often random and of relatively low amplitude. It can be caused by external sources or generated within the circuit itself. While it is impossible to eliminate electrical noise entirely, several strategies can be employed to reduce its impact.
One effective method to reduce electrical noise is to address the root causes, such as the power supply, an LDO, a switching regulator, or a resistor. For example, in an office setting, a laser copier/printer can cause voltage sags and transients that affect other loads on the same branch circuit. By identifying and mitigating these specific sources of noise, you can significantly improve circuit performance.
Another strategy is to utilise a Faraday cage, which is a shielded enclosure that isolates the circuit from external noise sources. This is particularly useful for protecting sensitive circuits from electromagnetic interference. Additionally, proper grounding techniques, such as ensuring all ground wires are at the same potential in a ground bus, can help prevent ground loops and reduce noise.
Twisted pair wiring is another technique that can reduce electromagnetic noise. By twisting the wires together, the loop size available for a magnetic field to induce a current is reduced, resulting in less overall noise. Similarly, notch filters or band-rejection filters can be employed to eliminate specific noise frequencies, such as power line frequencies that may interfere with sensitive circuits.
To address thermal noise, which is influenced by temperature, resistance, and bandwidth, using smaller resistors or employing low-current biasing techniques can be beneficial. Additionally, cooling the circuit can reduce thermal noise, although this is typically reserved for specialised applications such as radio telescopes.
In summary, reducing electrical noise involves a combination of strategies, including identifying and mitigating specific noise sources, utilising shielding and grounding techniques, employing twisted pair wiring and filters, and addressing thermal noise through component selection and cooling methods. By implementing these strategies, the impact of electrical noise on circuit performance can be minimised.
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Effects of electrical noise
Noise in electrical circuits refers to random variations in voltage or current that are usually of low amplitude and are always undesirable. These variations can be caused by various factors, both internal and external to the circuit, and can have several effects on the circuit's performance.
One of the effects of electrical noise is the degradation of circuit and system performance. Noise adds to or modifies the desired signal, resulting in reduced functionality. For example, in offices, the constant switching of a laser copier/printer between active and inactive modes can cause current surges and repetitive voltage sags. These sudden changes in current can also generate transients that affect other loads on the same branch circuit.
Electrical noise can also lead to data loss or corruption. Transient, high-frequency voltages, known as "line noise," can pass through a power supply and wipe out stored data or produce erroneous data output. This type of noise can be grouped into two categories: normal mode and common mode.
Additionally, electrical noise can interfere with sensitive circuits, such as audio circuits, producing undesirable sounds. Burst noise, for instance, is characterised by sudden transitions between voltage or current levels, resulting in popping or crackling sounds. Flicker noise, on the other hand, occurs in almost all electronic devices and is characterised by a frequency spectrum that falls off into higher frequencies, resulting in a pink spectrum.
Furthermore, electrical noise can be coupled into a circuit from external sources through inductive or capacitive coupling. This occurs when signals of different frequencies share the same non-linear medium, causing undesired interference on another channel. External noise sources can include lightning discharges, other electrical disturbances in nature, and man-made sources such as automobiles, aircraft, and high-voltage wires.
While it is impossible to eliminate noise entirely, there are strategies to mitigate its impact. For instance, a Faraday cage can be used to isolate a circuit from external noise sources, and careful circuit design can minimise intrinsic noise sources. Additionally, techniques such as twisted pair wiring and notch filters can reduce electromagnetic noise and eliminate specific noise frequencies, respectively.
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Measuring electrical noise
Noise in an electrical circuit refers to random variations in voltage or current, usually of low amplitude and always undesirable. This noise can be generated within the circuit itself or coupled into the circuit from external sources. While it is impossible to eliminate noise entirely, it can be minimised and its impact mitigated through various techniques.
Use Test Points and Probes:
Test points on a circuit board can be touched with a probe to measure noise. This method should be carefully designed and placed on the board to ensure accurate measurements. It is important to consider the quality of the board and the presence of noise sources, as they can affect the ease of measurement.
Control the Gain of the ADC:
By controlling the gain of an Analog-to-Digital Converter (ADC) and ensuring a well-designed ADC circuit, you can use it as a probe replacement to measure noise. This approach can delay the need for more expensive measurement equipment.
Noise Figure Calculation:
Every circuit has a noise figure, which is the amount of noise the circuit contributes. To calculate an amplifier's noise figure, you can measure the noise power at the input and output of the amplifier and find the difference. The noise figure is the difference between the calculated and measured noise power.
Use a Noise Source:
By introducing a known noise signal into the circuit, you can measure its output and calculate the noise contribution of a component, such as an amplifier. This technique helps determine how much noise a specific component adds to the circuit.
Use of DSOs and Analysers:
Digital Storage Oscilloscopes (DSOs) can capture, store, and display transient waveforms caused by current surges or voltage fluctuations. Analysers, such as the Fluke 43 PQ Analyzer, can also capture and record these events with time and date stamps.
Consider the Frequency Range:
Often, you only need to focus on the noise within a specific frequency range of interest. By ignoring noise outside this bandwidth, you can simplify the measurement process and concentrate on the relevant noise sources.
Use of Filters and Shielding:
Notch filters or band-rejection filters can eliminate specific noise frequencies. Additionally, shielding cables, similar to a Faraday cage, can protect sensitive circuits from unwanted noise by isolating them from external noise sources.
Modify Circuit Layout:
Improving the circuit layout and grounding can help address capacitive coupling issues. It is also important to avoid ground loops when grounding a circuit by ensuring all ground wires are at the same potential.
Reduce Thermal Noise:
Thermal noise is related to temperature, resistance, and bandwidth. It can be reduced by using smaller resistors, adding filters to limit bandwidth, or employing low-current biasing techniques.
Twist Wires in a Circuit:
Twisting wires in a circuit reduces electromagnetic noise by decreasing the loop size through which a magnetic field can induce a current. This technique ensures that there is no net noise current as the induced currents flow in opposite directions in alternate loops.
It is important to note that the specific techniques and equipment used for measuring electrical noise may vary depending on the circuit design, noise sources, and available resources.
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Frequently asked questions
Noise in an electrical circuit refers to random and undesirable variations in voltage or current.
There are several types of electrical noise, including thermal noise, burst noise, flicker noise, shot noise, and popcorn noise. Thermal noise is caused by temperature, resistance, and bandwidth. Higher temperatures and higher resistance lead to higher noise amplitude. Burst noise is caused by sudden transitions between voltage or current levels, while flicker noise, or 1/f noise, is characterised by a frequency spectrum that falls off into higher frequencies. Shot noise is more common in semiconductors, and popcorn noise is so-called because of the popping or crackling sounds it produces in audio circuits.
Electrical noise can be generated in the circuit itself or coupled into a circuit from external sources such as the environment, lightning discharges, or electrical disturbances in nature. Industrial noise is caused by sources such as automobiles, aircraft, ignition electric motors, and fluorescent lamps.
Electrical noise can be reduced by using techniques such as Faraday cages, improved circuit layout and grounding, shielding cables, twisted pair wiring, notch filters, and cooling of circuits.
