# Input impedance

**input resistanceload impedanceload resistanceinputloadimpedanceterminated**

The input impedance of an electrical network is the measure of the opposition to current (impedance), both static (resistance) and dynamic (reactance), into the load network that is external to the electrical source.wikipedia

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### Impedance matching

**matching networkimpedance matchimpedance mismatch**

If the impedance matches, the connection is known as a matched connection, and the process of correcting an impedance mismatch is called impedance matching.

In electronics, impedance matching is the practice of designing the input impedance of an electrical load or the output impedance of its corresponding signal source to maximize the power transfer or minimize signal reflection from the load.

### Buffer amplifier

**buffervoltage followercurrent buffer**

Voltage follower or impedance-matching transformers are often used for these effects.

A voltage buffer amplifier is used to transfer a voltage from a first circuit, having a high output impedance level, to a second circuit with a low input impedance level.

### Operational amplifier

**op-ampop ampoperational amplifiers**

The input impedance for high-impedance amplifiers (such as vacuum tubes, field effect transistor amplifiers and op-amps) is often specified as a resistance in parallel with a capacitance (e.g., 2.2MΩ ∥ 1pF).

;Finite input impedances : The differential input impedance of the operational amplifier is defined as the impedance between its two inputs; the common-mode input impedance is the impedance from each input to ground.

### Maximum power transfer theorem

**maximum power theoremMaximum powermaximize the power transfer**

The condition of maximum power transfer states that for a given source maximum power will be transferred when the resistance of the source is equal to the resistance of the load and the power factor is corrected by canceling out the reactance.

In radio frequency transmission lines, and other electronics, there is often a requirement to match the source impedance (at the transmitter) to the load impedance (such as an antenna) to avoid reflections in the transmission line that could overload or damage the transmitter.

### Impedance bridging

**bridging**

This is called impedance bridging.

When the output of a device (consisting of the voltage source V S and output impedance Z S in illustration) is connected to the input of another device (the load impedance Z L in the illustration), it is a bridging connection if the input impedance (Z L ) of the load device is much greater than (typically at least ten times) the output impedance (Z S ) of the source device.

### Nominal impedance

**Impedance50 Ω50-ohm coaxial cable**

In RF systems, typical values for line and termination impedance are 50 Ω and 75 Ω.

### Damping factor

**damping**

The load impedance (input impedance) and the source impedance (output impedance) are shown in the diagram.

### Output impedance

**Output resistancesource impedancesource resistance**

In modern signal processing, devices, such as operational amplifiers, are designed to have an input impedance several orders of magnitude higher than the output impedance of the source device connected to that input.

### Electrical network

**circuitelectrical circuitelectric circuit**

The input impedance of an electrical network is the measure of the opposition to current (impedance), both static (resistance) and dynamic (reactance), into the load network that is external to the electrical source. In AC circuits carrying power, the losses due to the reactive component of the impedance can be significant.

### Electrical resistance and conductance

**resistanceelectrical resistanceconductance**

The input impedance of an electrical network is the measure of the opposition to current (impedance), both static (resistance) and dynamic (reactance), into the load network that is external to the electrical source.

### Electrical reactance

**reactancereactivecapacitive reactance**

The input impedance of an electrical network is the measure of the opposition to current (impedance), both static (resistance) and dynamic (reactance), into the load network that is external to the electrical source.

### Thévenin's theorem

**Thévenin equivalentThéveninThevenin equivalent**

The Thévenin's equivalent circuit of the electrical network uses the concept of input impedance to determine the impedance of the equivalent circuit.

### Ohm's law

**ohmicOhmohmic losses**

If one were to create a circuit with equivalent properties across the input terminals by placing the input impedance across the load of the circuit and the output impedance in series with the signal source, Ohm's law could be used to calculate the transfer function.

### Power (physics)

**powermotive powerengine power**

In AC circuits carrying power, the losses due to the reactive component of the impedance can be significant.

### Complex conjugate

**complex conjugationconjugateconjugation**

When this occurs the circuit is said to be complex conjugate matched to the signals impedance.

### Transmission line

**transmission linestransmissiontransmission-line**

When the characteristic impedance of a transmission line does not match the impedance of the load network, the load network will reflect back some of the source signal.

### Standing wave

**standing wavesstationary wavestanding**

This can create standing waves on the transmission line.

### Signal processing

**signal analysissignalsignal processor**

In modern signal processing, devices, such as operational amplifiers, are designed to have an input impedance several orders of magnitude higher than the output impedance of the source device connected to that input.

### Amplifier

**amplifiersamplificationelectronic amplifier**

In modern signal processing, devices, such as operational amplifiers, are designed to have an input impedance several orders of magnitude higher than the output impedance of the source device connected to that input.

### Vacuum tube

**vacuum tubestubethermionic valve**

The input impedance for high-impedance amplifiers (such as vacuum tubes, field effect transistor amplifiers and op-amps) is often specified as a resistance in parallel with a capacitance (e.g., 2.2MΩ ∥ 1pF).

### Field-effect transistor

**FETfield effect transistorfield-effect transistors**

The input impedance for high-impedance amplifiers (such as vacuum tubes, field effect transistor amplifiers and op-amps) is often specified as a resistance in parallel with a capacitance (e.g., 2.2MΩ ∥ 1pF).

### Ohm

**Ωohmsmegohm**

### Farad

**microfaradFpF**

### Mains hum

**humbuckinghum60-cycle hum**

Pre-amplifiers designed for high input impedance may have a slightly higher effective noise voltage at the input (while providing a low effective noise current), and so slightly more noisy than an amplifier designed for a specific low-impedance source, but in general a relatively low-impedance source configuration will be more resistant to noise (particularly mains hum).

### Electrical breakdown

**dielectric breakdownbreakdowndisruptive discharge**

If this voltage exceeds the dielectric breakdown strength of the insulating material of the line then an arc will occur.