The reliability and efficiency of electronic systems depend on the fundamental role played by active and passive components. These components perform essential functions required to integrate new equipment into existing or new systems properly. While active components such as transistors and amplifiers require an external power source to supply energy to a circuit, passive components do not. Passive components provide a function integral to all these devices; they receive and store energy but do not require electricity. This article will discuss the significance of passive components, the challenges in their integration and advancements in their development.
ROLE AND COMMON TYPES OF PASSIVE COMPONENTS
Passive components are a core element in electronic systems, mainly because they do not require external power. They are indispensable to the functionality of electronic circuits. These components play a crucial role in managing the flow of the electrical current, protecting against voltage spikes and ensuring the overall reliability and performance of electrical devices. By filtering signals, matching impedance and conditioning signals, passive components contribute to the performance, stability and efficiency of electronic circuits. Without passive components to consume, store and release power, electronic systems cannot function.
Common types of passive components include:
- Resistors: Resistors control the electrical current by providing precise resistance, which is crucial for voltage division and signal conditioning. A resistor can only receive energy, which is dissipated as heat when the current runs continuously. This is essential for protecting sensitive components from damage and for controlling voltage levels in circuits. Resistors are common in consumer products such as electric stoves, heaters and toasters, as well as commercial and defense systems.
- Capacitors: Capacitors store and release electrical energy, which is essential for smoothing signals and filtering noise. Capacitors can filter out high frequency noise that could obstruct a circuit’s operation. They consist of two conductive plates separated by an insulating material called a dielectric. Capacitors are also used in a full range of consumer, commercial and defense products and systems.
- Inductors: An inductor stores energy in a magnetic field when an electrical current passes through it. It is also known as a reactor, choke or coil; it typically consists of a coil of wire wound around a core. Inductors resist changes in current and are used for energy storage, filtering and signal conditioning. They are critical in power supplies for filtering and energy storage, along with signal processing for noise suppression.
- RF filters, attenuators and terminations: These components provide essential RF connectivity and transmission functions, ensuring minimal signal loss and reflection within RF circuits and systems. Filters are used to reduce interference and block undesired frequencies by allowing or blocking specific signals. Attenuators reduce a signal’s power without reducing its quality, helping to protect systems that might not be able to handle input powers over a certain level. Terminations, also known as terminators or loads, are located at the end of a transmission line and prevent the reflection of RF signals back through the line. Figure 1 shows an example of an RF termination. This RF load handles 5 W of input power over the DC to 6 GHz frequency range. This version is equipped with a 2.2-5 male input connector.
Figure 1 PE6TR1162 DC to 6 GHz RF termination.
Other passive components include transformers, switches, circuit breakers and relays. Although a diode is typically classified as a passive component, it is constructed using semiconductor methods commonly associated with active components. Each of these functional components plays a unique role in maintaining the functionality and efficiency of electronic systems, so understanding these components is essential in the design and maintenance of electronic devices. Figure 2 shows a representative block diagram of a wireless transceiver. It is a good example of the widespread use of passive elements like filters, baluns and couplers. The diagram does not show individual components like resistors, capacitors and inductors that may be used to provide biasing, tuning and attenuation in some of the functional blocks shown.
Figure 2 Representative wireless transceiver block diagram. Source: ADI.
The representative wireless transceiver functional block diagram of Figure 2 is generic but contains an important feature. Generally speaking, whether passive or active, higher frequency components are more expensive. A common technique used in heterodyne transceivers, like that shown in Figure 2, to support higher operating frequencies is multiplying a lower frequency signal to the transmit frequency of interest and dividing the received signal to a lower frequency. This allows more of the conversion and processing to be done at lower frequencies. These multipliers/dividers typically also contain filters and other passive components.
Figure 3 Pasternack PE87FL1004 bandpass filter.
Figure 4 PE8739A bandpass filter.
Figure 3 shows a connectorized bandpass filter operating from 12.2 to 12.7 GHz, and Figure 4 shows a lower frequency connectorized bandpass filter operating from 4.4 to 4.8 GHz. While size and weight are important, especially in high volume commercial applications, performance and cost considerations will influence the best system solution for passive and active components.
