What is Impedance matching: Definition and 59 Discussions
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. A source of electric power such as a generator, amplifier or radio transmitter has a source impedance equivalent to an electrical resistance in series with a frequency-dependent reactance. Likewise, an electrical load such as a light bulb, transmission line or antenna has an impedance equivalent to a resistance in series with a reactance.
The maximum power theorem states that maximum power is transferred from source to load when the load resistance equals the source resistance and the load reactance equals the negative of the source reactance: the reactances cancel each other out with their opposing dependency on frequency. Another way of saying this using complex numbers is the load impedance must equal the complex conjugate of the source impedance. If this condition is met the two parts of the circuit are said to be impedance matched.
In a direct current (DC) circuit, the condition is satisfied if the load resistance equals the source resistance. In an alternating current (AC) circuit the reactance depends on frequency, so circuits which are impedance matched at one frequency may not be impedance matched if the frequency is changed. Impedance matching over a wide band will generally require complex, filter-like structures with many components except in the trivial case of constant source and load resistances when a transformer can be used.
In the case of a complex source impedance ZS and load impedance ZL, maximum power transfer is obtained when
Z
S
=
Z
L
∗
{\displaystyle Z_{\mathrm {S} }=Z_{\mathrm {L} }^{*}\,}
where the asterisk indicates the complex conjugate of the variable. Where ZS represents the characteristic impedance of a transmission line, minimum reflection is obtained when
Z
S
=
Z
L
{\displaystyle Z_{\mathrm {S} }=Z_{\mathrm {L} }\,}
The concept of impedance matching found first applications in electrical engineering, but is relevant in other applications in which a form of energy, not necessarily electrical, is transferred between a source and a load. An alternative to impedance matching is impedance bridging, in which the load impedance is chosen to be much larger than the source impedance and maximizing voltage transfer, rather than power, is the goal.
Hi All,
I am building a circuit that i need to get a better understanding of before jumping in head first, it says it requires an Impedance Matching Transformer.
I don't get this with the Attached Circuit, is it the whole Primary circuit has to match the whole Secondry Circuit Impedance...
Hi,
I'm having a little trouble understanding the concept of impedance matching to maximise energy transfer. I understand that the reactance of a capacitor is X_c= \frac{1}{\omega C } and that it is always 90 degrees lagging of the current in the complex plane which leads to a capacitors...
A friend of mine is having problems with a measurement signal he is getting from a Rogowski coil. When he changes the coaxial cable length the amplitude of the signal changes. It’s been a while since I’ve studied this type of thing but to me it sounded like an impedance mismatch issue and...
Hi.
I need to connect an antenna to a BPF (Band Pass Filter) and this one to a transceiver. The BPF purpose isn't to make matching, is to filter the input/output signals to the desired bandwidth.
I'm a little confuse and would like you to confirm my ideas, to help I made a sketch...
Our professor gave us some homework and one of the problem statements reads:
"Design an impedance matching network used to connect a 300 Ohm transmission line to a 50 Ohm transmission line."
Is this as simple as Zmatch = Sqrt(Z1*Z2) ? I'm wondering if there's something I'm missing...
Hi all, I'm currently studying up on transmission lines for my next midterm, and I stumble onto this problem.
Given information: A 800 MHz transmission line that is lossless
- Vmax, Vmin, V_L for a given load impedance R_L.
- Characteristic impedance of a line
- length of a line & \lambda...
Ok, need some help with the end part of this, here's the problem...
The relation between the impedance Z and the refractive index n of a dielectric is given by Z=1/n. Light traveling in free space enters a glass lens which has a refractive index of 1.5 for free space wavelength of 5.5E-7 m...
Hi,
I have a few 50 ohm loop antennas tuned to resonate at 13.56 MHz. (inductive RFID antenna). I would like to test one antenna´s influence on the other, so I think one approach is to connect one antenna directly to a signal generator.
Do I have to design any matching circuit between the...
if i want to connect a comparator chip's output (TTL) to Spartan2 FPGA board, can i directly do it, do i need to consider the impedance match? when i directly connect them, I will see the transition on the edge of the waveform stored (after FPGA processing, i save the output of FPGA and plot on...