Analogue electronics

Analogue electronics are systems that use continuously variable signals to carry information. This is different from digital electronics, where signals usually jump between only two specific levels. The term analogue comes from a Greek word meaning proportional. In these systems, there is a direct, proportional relationship between a signal and the voltage or current used to represent it. Every tiny change in the signal represents a different level of the phenomenon being measured. This makes analogue systems very sensitive to the physical world around them.

To work, these systems often rely on a transducer. A transducer is a device that converts one type of energy into another. For example, a microphone acts as a transducer by turning sound pressure into electrical signals. When a sound strikes a microphone, the variation in pressure creates a corresponding change in current or voltage. If the volume of the sound increases, the electrical fluctuation increases proportionally. Other ways to convey signals include modulation. In amplitude modulation (AM), the amplitude of a waveform is altered by the source information. In frequency modulation (FM), the frequency is changed instead. Other methods include phase modulation, which alters the phase of the carrier signal.

Analogue signals can be categorized by the components used to build them. Some circuits are entirely passive, meaning they consist only of resistors, capacitors, and inductors. Other circuits are active because they contain active elements like transistors. There is also a difference in how components are arranged. Traditional circuits use lumped elements, which are discrete, separate components. In contrast, distributed-element circuits are built from pieces of a transmission line. These different types allow engineers to build everything from simple sensors to complex radio receivers.

One major challenge in analogue electronics is inherent noise. Noise consists of random disturbances or variations in a signal. Some noise is caused by the random thermal vibrations of atomic particles. Other noise can come from crosstalk between different signals or from poorly designed components. Because every change in an analogue signal is meaningful, any disturbance appears as noise. As a signal is copied or sent over long distances, these variations can cause signal degradation. To fight this, engineers use shielding and low-noise amplifiers (LNA) to reduce disturbances.

Analogue and digital systems handle noise in very different ways. Analogue signals are said to "fail gracefully." This means that even with very high levels of noise, the signal can still contain intelligible information. Digital signals do not show much effect from noise until a certain threshold is reached. Once that limit is hit, digital systems fail catastrophically. In digital systems, signals are regenerated at each logic gate to remove noise. In analogue systems, signal loss is managed with amplifiers, but the amplifier itself adds more noise to the system according to its noise figure.

Precision in analogue systems is limited by physical factors. Shot noise in components creates a fundamental limit on how much detail a signal can show. To bridge the gap between the physical world and computers, engineers use converters. An analogue-to-digital converter (ADC) takes an analogue signal and changes it into a series of binary numbers. This is used in digital sound recording and data acquisition. To turn that data back into something we can hear or see, a digital-to-analogue converter (DAC) is used. The DAC takes binary numbers and converts them back into a continuous analogue signal.

Designing analogue circuits is often more difficult than designing digital ones. Digital hardware is highly standardized and can be mass-produced using repeated identical blocks. Analogue circuits are usually designed by hand because the specific application is built directly into the hardware. However, technology has helped make this easier. In the 1970s, IBM developed a simulator called ASTAP that used a sparse matrix method for circuit analysis. Today, engineers use software circuit simulators like SPICE to prototype designs much faster. Even in a digital world, every device that interacts with the real world still requires an analogue interface.