In our impression, resistors serve the purpose of impeding the flow of current.
But what about a 0-ohm resistor? What use do we have for a resistor that doesn't block current? In fact, 0-ohm resistors did not emerge at the outset, and most 0-ohm resistors are surface mount resistors. This is closely related to their applications.
During the time when through-hole double-sided board designs were still widely used in circuit boards, there wasn't much room for 0-ohm resistors to play a significant role. If a company wanted to save costs or for other reasons chose to use single-sided circuit boards, they would use jumper wires or vias to connect two separated parts of the circuit where routing was not possible.
As time progressed, the increasing use of surface mount components in large-scale industrial production led to the same issue when producing surface mount single-sided circuit boards. Jumper wires would be difficult to solder into the pads of surface mount components. This is where 0-ohm resistors came into play, allowing for a "leap" over finer traces, thereby reducing the complexity of the design.
For the same reason, in the past, jumpers and jumper caps were used on circuit boards for hardware-based on/off control during configuration. However, for surface mount circuit boards, it is difficult to use machines for the uniform installation of jumpers. Instead, the combination of empty pads and 0-ohm resistors can serve the same purpose as jumpers, providing a configuration function during production.
On the other hand, traditional jumpers, when not connected with jumper caps, can radiate interference signals at higher signal frequencies on both ends, which is inferior to empty pads in this regard.
In fact, besides these reasons, there are various additional benefits of using 0-ohm resistors.
For instance, they can serve as leads for grounding points and construct current loops. There are also reasons that are harder to foresee, such as facilitating easy removal for measurement or using unlabeled 0-ohm resistors to prevent reverse engineering of circuit boards. These all belong to additional applications that have been developed. Normally, in the process of DIY, we seldom use 0-ohm resistors. However, for those on circuit boards, we should also understand their functions.
It serves no functional purpose in the circuit and is only included on the PCB for reasons such as ease of debugging or compatibility design.
It can be used as a jumper. If a certain section of the circuit is not needed, simply omit the resistor (without affecting the appearance).
When the circuit parameters for matching are uncertain, a 0-ohm resistor can be used as a placeholder. During actual debugging, once the parameters are determined, it can be replaced with a component of a specific value.
When measuring the current consumption of a particular circuit section, the 0-ohm resistor can be removed and an ammeter connected in its place, facilitating the measurement of current consumption.
During wiring, if routing is truly impossible, a 0-ohm resistor can be added.
In high-frequency signals, it can function as an inductor or capacitor (depending on the characteristics of the external circuit). As an inductor, it is primarily used to address EMC issues, such as between ground planes, power supplies, and IC pins.
Single-point grounding (referring to the separation of protective grounding, working grounding, and DC grounding on equipment into independent systems).
Fuse function.
- Single-Point Grounding for Analog and Digital Grounds
Ultimately, all grounds, regardless of type, should be connected together and grounded to the earth. If they are not connected, they become "floating grounds," which can lead to potential differences and the accumulation of charges, causing static electricity.
Ground serves as the reference point for zero potential, and all voltages are measured relative to ground. Therefore, the grounding standards must be consistent, and all types of grounds should be short-circuited together.
It is believed that the earth can absorb all charges and remain stable, serving as the ultimate reference point for grounding. Although some boards are not directly grounded, power plants are grounded, and the power supply on the board will ultimately return to the power plant and be grounded.
Directly connecting analog and digital grounds over a large area can lead to mutual interference. Not short-circuiting them is also inappropriate. There are four methods to address this issue, as mentioned earlier:
(1) Connect using ferrite beads;
(2) Connect using capacitors;
(3) Connect using inductors;
(4) Connect using 0-ohm resistors.
The equivalent circuit of a ferrite bead resembles a band-stop filter, which significantly suppresses noise at a specific frequency point. When using them, it is necessary to estimate the noise frequency beforehand to select the appropriate type. Ferrite beads are not suitable for situations where the frequency is uncertain or unpredictable.
Capacitors block DC and pass AC, creating a floating ground. Inductors are bulky and have many stray parameters, making them unstable.
A 0-ohm resistor acts as a very narrow current path, effectively limiting loop currents and suppressing noise. Resistors have attenuation effects across all frequency bands (0-ohm resistors also have impedance), which is an advantage compared to ferrite beads.
- Used in Current Loops for Bridging
When the ground plane is divided, it causes the shortest return path for signals to be broken. At this point, the signal loop has to bypass, forming a large loop area, which intensifies the influence of electric and magnetic fields, making it prone to interference or being interfered with. Bridging a 0-ohm resistor over the divided area can provide a shorter return path and reduce interference.
- General Circuit Configuration: Avoid Using Jumpers and DIP Switches on Products
Sometimes users may change settings arbitrarily, which can lead to misunderstandings. To reduce maintenance costs, 0-ohm resistors should be used instead of jumpers and other components soldered onto the board. Unused jumpers can act as antennas at high frequencies, and using surface-mount resistors is more effective.
- Other Uses
- Bridging during wiring;
- For debugging/testing purposes;
- Temporarily replacing other surface-mount devices;
- Serving as temperature compensation devices;
More often than not, they are used for EMC countermeasures. Additionally, 0-ohm resistors have smaller parasitic inductance than vias, and vias can also affect the ground plane (due to the need for drilling holes).
Furthermore, different sizes of 0-ohm resistors allow for different currents to pass through them. Generally, 0603 resistors can handle 1A, and 0805 resistors can handle 2A. Therefore, different sizes are selected based on the current requirements. When reserving space for ferrite beads, inductors, and other components, the packaging must be based on the size of the component, so 0603, 0805, and other sizes are available.
