Lumped and Distributed are descriptions of how components and parameters (resistance, capacitance, and inductance) are considered in the analysis of a circuit.
1. Lumped Elements:
- A lumped element model is one in which all the effects of a circuit (such as resistance, capacitance and inductance) are imagined to be concentrated (or lumped) at certain points in the circuit.
- This implies that components are considered as discrete, singular items that have values that are well defined.
- Lumped element model is accurate when the physical dimensions of the circuit are small relative to the wavelength of the signals in the circuit (e.g. at low frequencies). Here the time delays and wave propagation effects in the circuit can be ignored.
- Examples: In normal circuit analysis resistors, capacitors, and inductors are analysed as lumped elements, where all the characteristics of the element are concentrated at a point.
Lumped system assumptions:
- Propagation of signals (no time delay) is instantaneous.
- Components are supposed to take no physical space (idealized).
2. Distributed Elements:
- In a distributed element model, the parameters (resistance, capacitance and inductance) are continuous functions of the length of a component or transmission line.
- The model is applied when the physical size of a system is similar to the signals in the system (as in high-frequency circuits or long transmission lines) and one must take into account the dependence of these quantities along the structure.
- Examples: Transmission lines Antennas Waveguides are commonly modelled with distributed elements in these systems, the voltage, current, resistance and capacitance are continuous functions of the length of the component.
Distributed system assumptions:
- A signal propagation delay is taken into account.
- The parameters (such as resistance, inductance, capacitance) depend on the position along the component.