1. A PCB board is composed of multiple conductors connected in parallel, such as traces, separated by insulators. These traces, together with the dielectric material, form a capacitor, resulting in unwanted parasitic capacitance or stray capacitance effects.
2. The parasitic elements in a PCB can include parasitic capacitance, parasitic resistance, and parasitic inductance. When traces are closely spaced, the parasitic capacitance effect becomes particularly pronounced in high-frequency boards. This effect is entirely unwanted and can adversely impact device functionality. It can lead to issues such as crosstalk, EMI, and compromised signal integrity. PCB designers working with high-frequency, high-data-rate, and mixed-signal boards must account for parasitic capacitance and inductance effects when designing the PCB layout.
3. In the following section, we will explore the definition of parasitic capacitance and its impact on circuit boards.
4. What is parasitic capacitance in a PCB?
5. The closely placed PCB conductors act as a virtual capacitor, resulting in parasitic capacitance effects.
6. Parasitic capacitance, also known as stray capacitance, arises from a virtual capacitor formed between two traces separated by a dielectric. It occurs due to the potential difference generated when current-carrying traces are in close proximity. To learn more, read about the role of line current capacity in PCB design.
1. This effect can occur even if the conductors are properly insulated. Since there is no ideal circuit, parasitic capacitance cannot be completely avoided.
2. The charge and discharge cycle in a capacitor.
3. Parasitic capacitance is an inherent characteristic of conductors. It represents the amount of charge stored per unit potential change. The formula for calculating parasitic capacitance is C = q/v, where C is the capacitance in farads, v is the voltage in volts, and q is the charge in coulombs.
4. For a constant electrical signal that does not change over time, dv/dt = 0, which indicates no change in potential; thus, i = 0.
5. If a capacitor is present in the circuit loop, dv/dt will converge to a fixed value, resulting in potential changes and current generation; thus, i ≠ 0.
6. Trace capacitance calculation
7. The capacitance of a parallel plate capacitor is given by C = (kA/11.3d) pF, where C is the capacitance, A is the plate area in cm², k is the relative permittivity of the plate material, and d is the distance between the plates in cm.
8. Modeling of PCB parasitic components at high frequencies
9. The parasitic capacitance effect is significant in high-frequency circuit boards. At low frequencies, parasitic components can often be ignored as they do not substantially impact system function. Each pad on the circuit board has its parasitic capacitance, and each trace has parasitic inductance. Pads also introduce parasitic resistance, which contributes to IR loss. Parasitic capacitance may occur between the PCB, bare board, PCBA, assembly board, and conductors in the component package, especially with surface mount devices (SMD).
10. Since intrinsic capacitor plates have a potential difference, there is an opportunity for current flow. Charge storage between capacitor plates is not necessary for current flow; it requires a potential difference. An increase in this potential difference can lead to a corresponding decrease in electron flow to the load, negatively affecting signal integrity.
11. What is the difference between stray capacitance and parasitic capacitance?
12. The term stray capacitance is often used interchangeably with parasitic capacitance. However, parasitic capacitance implies it will hinder circuit operation, while stray capacitance refers to the introduction of unwanted capacitance.
13. What is stray capacitance?
14. Stray capacitance arises from the virtual capacitance between two PCB conductors and the influence of the surrounding environment. It is not always perceptible, hence the term “stray capacitance.”
15. What is parasitic resistance in PCB?
16. Parasitic resistances are connected in series along traces or exist as shunts between conductive elements.
17. What is parasitic inductance in PCB?
18. Parasitic inductances occur along traces, behaving similarly to actual inductors by storing and dissipating electrical energy. All conductors are inherently inductive, and at high frequencies, even relatively short wires or PCB traces can exhibit significant inductance.
19. Parasitic capacitance effects can include crosstalk, noise, poor feedback from the output, and the formation of resonant circuits. Therefore, attention must be given to overall PCB design, particularly the layout. Careful placement of conductors is essential.
20. Parasitic elements include inductances formed by package leads, long traces, pad-to-ground, pad-to-power plane, and pad-to-line capacitors, including interactions with vias. Understanding parasitic elements is crucial as they threaten circuit performance—unwanted yet inevitable, but controllable.
21. In high-speed circuits, even a few tenths of a picofarad can affect performance. For example, a 1pF parasitic capacitance at the inverting input can cause a 2dB peak in the frequency domain. Exceeding 1pF may lead to instability and oscillation.
22. Capacitors block low-frequency and DC signals while allowing high-frequency signals to pass in electronic circuits. This characteristic—along with the rapid discharge of capacitors—contributes to stray capacitance issues in high-speed circuits. Stray capacitance can introduce EMI or noise, propagating along wires and cables or transferring to adjacent traces. While it is generally impossible to eliminate stray capacitance, effective PCB layout techniques can mitigate its effects.
23. Avoid parallel routing: Parallel routing creates the largest area between two metals, resulting in the highest capacitance between them.
2. The parasitic elements in a PCB can include parasitic capacitance, parasitic resistance, and parasitic inductance. When traces are closely spaced, the parasitic capacitance effect becomes particularly pronounced in high-frequency boards. This effect is entirely unwanted and can adversely impact device functionality. It can lead to issues such as crosstalk, EMI, and compromised signal integrity. PCB designers working with high-frequency, high-data-rate, and mixed-signal boards must account for parasitic capacitance and inductance effects when designing the PCB layout.
3. In the following section, we will explore the definition of parasitic capacitance and its impact on circuit boards.
4. What is parasitic capacitance in a PCB?
5. The closely placed PCB conductors act as a virtual capacitor, resulting in parasitic capacitance effects.
6. Parasitic capacitance, also known as stray capacitance, arises from a virtual capacitor formed between two traces separated by a dielectric. It occurs due to the potential difference generated when current-carrying traces are in close proximity. To learn more, read about the role of line current capacity in PCB design.
1. This effect can occur even if the conductors are properly insulated. Since there is no ideal circuit, parasitic capacitance cannot be completely avoided.
2. The charge and discharge cycle in a capacitor.
3. Parasitic capacitance is an inherent characteristic of conductors. It represents the amount of charge stored per unit potential change. The formula for calculating parasitic capacitance is C = q/v, where C is the capacitance in farads, v is the voltage in volts, and q is the charge in coulombs.
4. For a constant electrical signal that does not change over time, dv/dt = 0, which indicates no change in potential; thus, i = 0.
5. If a capacitor is present in the circuit loop, dv/dt will converge to a fixed value, resulting in potential changes and current generation; thus, i ≠ 0.
6. Trace capacitance calculation
7. The capacitance of a parallel plate capacitor is given by C = (kA/11.3d) pF, where C is the capacitance, A is the plate area in cm², k is the relative permittivity of the plate material, and d is the distance between the plates in cm.
8. Modeling of PCB parasitic components at high frequencies
9. The parasitic capacitance effect is significant in high-frequency circuit boards. At low frequencies, parasitic components can often be ignored as they do not substantially impact system function. Each pad on the circuit board has its parasitic capacitance, and each trace has parasitic inductance. Pads also introduce parasitic resistance, which contributes to IR loss. Parasitic capacitance may occur between the PCB, bare board, PCBA, assembly board, and conductors in the component package, especially with surface mount devices (SMD).
10. Since intrinsic capacitor plates have a potential difference, there is an opportunity for current flow. Charge storage between capacitor plates is not necessary for current flow; it requires a potential difference. An increase in this potential difference can lead to a corresponding decrease in electron flow to the load, negatively affecting signal integrity.
11. What is the difference between stray capacitance and parasitic capacitance?
12. The term stray capacitance is often used interchangeably with parasitic capacitance. However, parasitic capacitance implies it will hinder circuit operation, while stray capacitance refers to the introduction of unwanted capacitance.
13. What is stray capacitance?
14. Stray capacitance arises from the virtual capacitance between two PCB conductors and the influence of the surrounding environment. It is not always perceptible, hence the term “stray capacitance.”
15. What is parasitic resistance in PCB?
16. Parasitic resistances are connected in series along traces or exist as shunts between conductive elements.
17. What is parasitic inductance in PCB?
18. Parasitic inductances occur along traces, behaving similarly to actual inductors by storing and dissipating electrical energy. All conductors are inherently inductive, and at high frequencies, even relatively short wires or PCB traces can exhibit significant inductance.
19. Parasitic capacitance effects can include crosstalk, noise, poor feedback from the output, and the formation of resonant circuits. Therefore, attention must be given to overall PCB design, particularly the layout. Careful placement of conductors is essential.
20. Parasitic elements include inductances formed by package leads, long traces, pad-to-ground, pad-to-power plane, and pad-to-line capacitors, including interactions with vias. Understanding parasitic elements is crucial as they threaten circuit performance—unwanted yet inevitable, but controllable.
21. In high-speed circuits, even a few tenths of a picofarad can affect performance. For example, a 1pF parasitic capacitance at the inverting input can cause a 2dB peak in the frequency domain. Exceeding 1pF may lead to instability and oscillation.
22. Capacitors block low-frequency and DC signals while allowing high-frequency signals to pass in electronic circuits. This characteristic—along with the rapid discharge of capacitors—contributes to stray capacitance issues in high-speed circuits. Stray capacitance can introduce EMI or noise, propagating along wires and cables or transferring to adjacent traces. While it is generally impossible to eliminate stray capacitance, effective PCB layout techniques can mitigate its effects.
23. Avoid parallel routing: Parallel routing creates the largest area between two metals, resulting in the highest capacitance between them.
