What is Passive Device？

In every industry, including the field of electronic components, there is a sense of correspondence or distinction between different types of products. In electronics, we often refer to passive device and active devices as corresponding counterparts. But what is passive device and active devices，and how to truly distinguish these two categories?

Definitions and Basic Characteristics

If an electronic component operates without any internal power source, it is classified as a passive component. From the perspective of digital circuit properties, passive components have two fundamental characteristics:

● Energy Interaction: They either consume electrical energy or convert it into different forms of energy.

● Operational Independence: They can function correctly with just an input signal, without the need for an external power supply.

In contrast, if an electronic component operates with an internal power source present, it is known as an active component. The key characteristics of active components, in terms of digital circuit properties, include:

● Energy Consumption: They also consume electrical energy themselves.

● Power Requirement: In addition to receiving an input signal, they require an external power source to operate properly.

From these definitions, we can deduce that active and passive components have fundamentally different requirements and modes of operation within simple circuits. Active components rely on additional power sources to perform their functions, such as amplification and signal processing, whereas passive components operate independently of external electric power, focusing instead on energy management tasks like storage and dissipation.

Common Passive Communication Components

Resistors

A resistor is a passive component that resists the flow of electrical current. It functions by providing resistance within a circuit, thus regulating current flow. Resistors are primarily used for reducing voltage, dividing voltage, or limiting flow of current in circuits, but they also serve as loads, feedback elements, coupling, and isolation components in certain applications. In schematic diagrams, resistors are represented by the letter "R," and their standard unit of measurement is the ohm (Ω), with commonly used multiples like kilo-ohms (KΩ) and mega-ohms (MΩ). For reference:

● 1 KΩ = 1,000 Ω

● 1 MΩ = 1,000 KΩ

Capacitors

Capacitors are another ubiquitous passive component in electronic circuits, used for storing electrical energy. Constructed from two conductors separated by an insulating material, capacitors store electric charge when a voltage is applied across them. They release energy once the voltage is removed, provided there’s a closed circuit. Capacitors block direct current (DC) while allowing AC current to pass, with greater efficiency at higher frequencies. In circuits, capacitors are often used for coupling, bypass filtering, feedback, timing, and oscillation. The symbol for capacitance is "C," and its unit is the farad (F), with common subunits like microfarads (μF) and picofarads (pF):

● 1 F = 1,000,000 μF = 10^6 μF = 10^12 pF

● 1 μF = 1,000,000 pF

Inductors

Inductors, similar to capacitors, are energy-storing electronic devices made typically from coils of wire. When AC voltage is applied across the coil, it generates an electromotive force that opposes changes in electric current, a property known as inductive reactance. Inductive reactance is proportional to the inductance and frequency of digital signal. While inductors do not impede direct current (excluding any DC resistance of the coil itself), they find significant use in circuits for blocking high-frequency currents, transforming voltages, coupling signals, and, in combination with capacitors, for tuning, filtering, frequency selection, and division. Inductors are represented by the letter "L" in schematics, and their unit of measurement is the henry (H), with subunits including millihenrys (mH) and microhenrys (μH):

● 1 H = 1,000 mH

● 1 mH = 1,000 μH

Inductors are central in electromagnetic induction and conversion technologies, with transformers being one of the most common applications of inductance principles.

Differences Between Passive and Active Electronic Components

Passive and active components represent two fundamental types of elements within electronic circuits, distinguished primarily by their energy handling capabilities and circuit functions.

Energy Source

● Passive Components: These do not have the ability to amplify or generate energy. They operate using the existing energy within the circuit, performing tasks without altering the intrinsic electrical power level.

● Active Components: These can actively amplify electrical signals or generate energy. They utilize an external power source to enhance signal amplitude and introduce additional energy into the circuit.

Signal Amplification

● Passive Components: They cannot increase the amplitude of electrical signals. Their role is more about controlling the flow and distribution of energy rather than enhancing it.

● Active Components: Devices like transistors and amplifiers can increase the amplitude of electrical signals, thus boosting signal strength.

Functionality

● Passive Components: Primarily involved in the adjustment, distribution, and regulation of circuits. They control current, voltage, and power gain, and are essential for impedance matching, energy storage, filtering, and signal coupling.

● Active Components: Offer a wide range of functionalities, including generating, amplifying, and controlling electrical signals. They are crucial for operations that require signal modification and enhancement.

Examples

● Common Passive Components: Resistors, capacitors, inductors, and transformers. These are utilized for adjusting circuit parameters, storing energy, and transmitting signals.

● Common Active Components: Transistors, integrated circuits, amplifiers. These components have the ability to actively amplify signals, generate energy, and control circuit dynamics.

In summary, while passive components manage and condition the existing electrical environment, active components dynamically alter and enhance it. Both types of electrical components are typically used in conjunction to build complex electronic systems and circuit designs, each contributing their unique properties to achieve desired performance outcomes.

Future Directions for Passive Components

1.Integrated Modularity: One of the key trends in the future development of passive components is integrated modularity. This approach combines both active components or modules and passive components into a unified system, achieving miniaturization and cost reduction simultaneously. Techniques facilitating this integration include Low Temperature Co-fired Ceramic (LTCC), thin-film technology, semiconductor wafer technology, and multi-layer circuit board technology.

2.Miniaturization: The wireless industry’s demand for smaller and lighter electronic devices drives the miniaturization trend for passive components. Micro-Electro-Mechanical Systems (MEMS) play a crucial role here, enabling radio frequency components to become smaller, more cost-effective, more powerful, and easier to integrate.

3.Packaging Effects: Compared to conventional surface-mounted passive components, integrating components within packaging can significantly enhance system reliability. This integration shortens conductive paths, reduces parasitic effects, lowers costs, and decreases component size. Packaging innovation thus holds substantial promise for improving performance and efficiency in electronic systems.

These directions indicate a robust trajectory toward more efficient, compact, and integrated passive components, meeting the evolving demands of modern technological applications.