In PCB board design, especially in high-frequency circuits, engineers often encounter irregular and abnormal phenomena caused by ground wire interference. This paper analyzes the causes of ground wire interference, elaborates on three specific types of such interference, and proposes practical solutions based on experience. These anti-jamming techniques have demonstrated effective results in real-world applications, ensuring successful operation of systems in the field.
In single-chip microcomputer systems, the PCB (printed circuit board) serves as a crucial component for supporting circuit elements and establishing electrical connections between components and devices. During the conduction process, impedance plays a critical role. The presence of inductive components in wires can impact voltage signal transmission, while resistive components affect current signal transmission. Inductive effects are particularly pronounced in high-frequency lines. It is essential to recognize and mitigate the influence of ground impedance.
1. The distinction between resistance and impedance Resistance and impedance are two distinct concepts. Resistance refers to the opposition of a wire to DC current, while impedance refers to the opposition to AC current, primarily caused by wire inductance. Since ground wires inherently exhibit impedance, their resistance when measured with a multimeter typically reads in milliohms (mmΩ). For instance, consider a wire on a PCB measuring 10 cm in length, 1.5 mm in width, and 50 μm in thickness. The impedance can be calculated as follows: ( R = rho frac{L}{s} ) (Ω), where ( L ) is the wire length (m), ( s ) is the cross-sectional area (mm²), and ( rho = 0.02 ) represents resistivity. Hence, the wire’s resistance approximates 0.026 Ω. When a wire is sufficiently distant from others and much longer than its width, its self-inductance may reach 0.8 μH/m. Consequently, the inductance of a 10 cm wire measures 0.08 μH. To determine the wire’s inductive reactance, use the formula: ( XL = 2πfL ), where ( f ) signifies the signal’s frequency (Hz), and ( L ) represents the wire’s self-inductance per unit length (H). As such, the inductive reactance values at both high and low frequencies are calculated individually. In practical circuits, pulse signals frequently cause electromagnetic interference, and since these signals comprise numerous high-frequency elements, they generate substantial noise voltage on the ground wire. According to the aforementioned formulas, wire resistance surpasses wire inductance when transmitting low-frequency signals. In contrast, digital circuits operate at notably high frequencies, rendering wire inductance significantly greater than wire resistance when processing high-frequency signals. Thus, the influence of ground impedance on digital circuits is markedly pronounced, leading to considerable voltage drops when minute currents traverse minute resistors, thereby causing circuitry malfunctions.
2. Mechanism of ground wire interference 2.1 Ground loop interference Ground loop interference frequently manifests between remotely located devices connected by extended cables. This common interference results from ground wire impedance. Current flowing through the ground wire induces a corresponding voltage, termed ground wire noise. This voltage subsequently engenders ground loop currents, inducing ground loop interference. Due to variances in the ground potentials of two devices, a ground voltage arises. Driven by this voltage, current courses through the loop composed of “device 1, interconnecting cable, device 2, and ground.” Due to circuit imbalances, dissimilar currents traverse each wire, yielding a differential mode voltage that interferes with circuit operation. Occasionally, disconnecting a device’s ground wire suffices to mitigate interference since this action severs the ground loop. Such occurrences are common during low-frequency interference. Conversely, disconnecting the ground wire proves ineffectual at higher interference frequencies.
2.2 Common impedance interference In digital circuits, the high signal frequencies often entail considerable ground wire impedance. Consequently, when multiple circuits share a single ground wire segment, the operating currents of one circuit may modulate the ground potential of another, thereby causing signal leakage between circuits—a phenomenon known as common impedance coupling. Addressing this interference involves either reducing the shared ground wire’s impedance or employing single-point grounding to wholly eliminate common impedance. Figure 2 illustrates a basic four-gate circuit configuration. If gate 1 transitions from high to low output, the circuit’s parasitic capacitance (potentially supplemented by an input filter capacitor for gate 2) discharges through gate 1 to the ground wire. Owing to the ground wire’s impedance, this discharge generates a peak voltage on the ground line. Concurrently, if gate 3 outputs a low signal, this peak voltage propagates to gate 3’s output terminal and gate 4’s input terminal. Should this voltage’s amplitude surpass gate 4’s noise threshold, it triggers gate 4 malfunction.
2.3 Ground loop electromagnetic coupling interference The “ground loop” surrounds a defined area. According to electromagnetic induction principles, a varying magnetic field within this enclosed zone elicits induced currents, thereby causing interference. Since spatial magnetic field variations are ubiquitous, larger enclosed areas intensify interference severity.
3. Methods to mitigate ground wire interference 3.1 Resolving ground loop interference Resolving ground loop interference hinges on three core strategies: reducing ground wire impedance to diminish interference voltage, though this tactic fails to counter secondarily induced ground loop interference. Alternatively, altering grounding configurations to interlink chassis ground wires, or implementing single-point grounding to eliminate ground loops entirely. Augmenting ground loop impedance achieves a comparable outcome, thereby curtailing ground loop current. Infinite impedance precludes ground loops, obviating the need for grounded cables. Accordingly, proposed solutions tackle the scourge of ground loop interference.
In single-chip microcomputer systems, the PCB (printed circuit board) serves as a crucial component for supporting circuit elements and establishing electrical connections between components and devices. During the conduction process, impedance plays a critical role. The presence of inductive components in wires can impact voltage signal transmission, while resistive components affect current signal transmission. Inductive effects are particularly pronounced in high-frequency lines. It is essential to recognize and mitigate the influence of ground impedance.
1. The distinction between resistance and impedance Resistance and impedance are two distinct concepts. Resistance refers to the opposition of a wire to DC current, while impedance refers to the opposition to AC current, primarily caused by wire inductance. Since ground wires inherently exhibit impedance, their resistance when measured with a multimeter typically reads in milliohms (mmΩ). For instance, consider a wire on a PCB measuring 10 cm in length, 1.5 mm in width, and 50 μm in thickness. The impedance can be calculated as follows: ( R = rho frac{L}{s} ) (Ω), where ( L ) is the wire length (m), ( s ) is the cross-sectional area (mm²), and ( rho = 0.02 ) represents resistivity. Hence, the wire’s resistance approximates 0.026 Ω. When a wire is sufficiently distant from others and much longer than its width, its self-inductance may reach 0.8 μH/m. Consequently, the inductance of a 10 cm wire measures 0.08 μH. To determine the wire’s inductive reactance, use the formula: ( XL = 2πfL ), where ( f ) signifies the signal’s frequency (Hz), and ( L ) represents the wire’s self-inductance per unit length (H). As such, the inductive reactance values at both high and low frequencies are calculated individually. In practical circuits, pulse signals frequently cause electromagnetic interference, and since these signals comprise numerous high-frequency elements, they generate substantial noise voltage on the ground wire. According to the aforementioned formulas, wire resistance surpasses wire inductance when transmitting low-frequency signals. In contrast, digital circuits operate at notably high frequencies, rendering wire inductance significantly greater than wire resistance when processing high-frequency signals. Thus, the influence of ground impedance on digital circuits is markedly pronounced, leading to considerable voltage drops when minute currents traverse minute resistors, thereby causing circuitry malfunctions.
2. Mechanism of ground wire interference 2.1 Ground loop interference Ground loop interference frequently manifests between remotely located devices connected by extended cables. This common interference results from ground wire impedance. Current flowing through the ground wire induces a corresponding voltage, termed ground wire noise. This voltage subsequently engenders ground loop currents, inducing ground loop interference. Due to variances in the ground potentials of two devices, a ground voltage arises. Driven by this voltage, current courses through the loop composed of “device 1, interconnecting cable, device 2, and ground.” Due to circuit imbalances, dissimilar currents traverse each wire, yielding a differential mode voltage that interferes with circuit operation. Occasionally, disconnecting a device’s ground wire suffices to mitigate interference since this action severs the ground loop. Such occurrences are common during low-frequency interference. Conversely, disconnecting the ground wire proves ineffectual at higher interference frequencies.
2.2 Common impedance interference In digital circuits, the high signal frequencies often entail considerable ground wire impedance. Consequently, when multiple circuits share a single ground wire segment, the operating currents of one circuit may modulate the ground potential of another, thereby causing signal leakage between circuits—a phenomenon known as common impedance coupling. Addressing this interference involves either reducing the shared ground wire’s impedance or employing single-point grounding to wholly eliminate common impedance. Figure 2 illustrates a basic four-gate circuit configuration. If gate 1 transitions from high to low output, the circuit’s parasitic capacitance (potentially supplemented by an input filter capacitor for gate 2) discharges through gate 1 to the ground wire. Owing to the ground wire’s impedance, this discharge generates a peak voltage on the ground line. Concurrently, if gate 3 outputs a low signal, this peak voltage propagates to gate 3’s output terminal and gate 4’s input terminal. Should this voltage’s amplitude surpass gate 4’s noise threshold, it triggers gate 4 malfunction.
2.3 Ground loop electromagnetic coupling interference The “ground loop” surrounds a defined area. According to electromagnetic induction principles, a varying magnetic field within this enclosed zone elicits induced currents, thereby causing interference. Since spatial magnetic field variations are ubiquitous, larger enclosed areas intensify interference severity.
3. Methods to mitigate ground wire interference 3.1 Resolving ground loop interference Resolving ground loop interference hinges on three core strategies: reducing ground wire impedance to diminish interference voltage, though this tactic fails to counter secondarily induced ground loop interference. Alternatively, altering grounding configurations to interlink chassis ground wires, or implementing single-point grounding to eliminate ground loops entirely. Augmenting ground loop impedance achieves a comparable outcome, thereby curtailing ground loop current. Infinite impedance precludes ground loops, obviating the need for grounded cables. Accordingly, proposed solutions tackle the scourge of ground loop interference.
