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.
The only thing I could think of was using Q=sqrt(6000/50)-1 = 10.9, which then gets me XL=545 and XC=550, or 96.4nH, and 0.32pF at resonance of 900Mhz. I tried seeing if Zin=Zout equation would bring me close, so I tried Z=545+(50-550)=45, then XL for 38.5nH was 217.7, and XC for 2.4pF was 74...
Assume we have a network consisting of a source with impedance ##Z_S## and load with impedance ##Z_L## and
we want to perform impedance matching on them in order to obtain the maximum power transfer:
Note that in practice there may occur sitations where causes more harm than profit (see eg...
Assume we have a general rf system where source with impedance ##Z_S##
transfers a signal to a load with impedance ##Z_L## through a transmission
line with impedance ##Z_T##. We want to match this system
in order to maximize it's effiency:
In
https://en.wikipedia.org/wiki/Impedance_matching...
Which role plays an additional capacity in a receiver circuit between the antenna and the matching-box part like in this example (found in https://www.frostburg.edu/personal/latta/ee/twinplex/schematic/twinplexschematic.html):
Is it necessary for this receiver circuit or just optional? What...
Here is a common CE-CC cascade amplifier-
Here, the output of the emitter amplifier is directly connected to Q2, without any coupling capacitor or any voltage divider bias. This may harm the base-emitter junction of Q2 in case of unwanted output voltage from Q1 collector. But in that case, the...
The WSM 50 Kilowatt AM station in Nashville TN, has been transmitting using the same ~950ft 5/8 wave Blaw Knox Diamond antenna, since 1929. The 5/8 wave vertical had some horizon gain over a 1/4 wave vertical so theoretically will serve distant listeners better. It was found though that...
Hi all,
I'm trying to understand basics of radiofrequency (RF) coil development for magnetic resonance imaging (MRI).
For example, the problem is to develop simple surface single-loop RF coil tuned to 100 MHz.
In program Coil32, I set the following parameters:
diameter of the loop D = 20 mm...
I am just a bit confused as to how impedance is matched with RF connectors such as type-N or BNC connectors. I know Coaxial cabling and RF connectors come in common impedance ratings like 50 or 75 ohm but how is this all matched properly? For example many people have told me that when using...
Hi all,
I am currently working on a project where the output/load consists of both a variable inductance and variable resistance, whilst the circuit driving this load is a class E radio frequency (RF) power amplifier with low resistance but relatively high/medium reactance (attempting to design...
Homework Statement
Say you connect Circuit A with low output impedance to circuit B with high input impedance. Why does this cause minimal voltage drop compared to connecting them the other way around (high output to low input).
Homework Equations
P = V^2/R
P = IV
The Attempt at a Solution
I...
Dear all,
is there anyone with plasma background?
I am developing an algorithm for a plasma impedance L type matching network.
Initially, I set the Load and Tune units to some specific positions. The algorithm is simply tuning a possible minimum SWR starting from the initial position...
Hello,
I'm trying to get some feedback on my circuit design (picture below). I am attempting to use a differential op amp to impedance match a 100 ohm transmission line. The transmission line is CAT6A twisted pair. I'm using CAT6A as a feed through into a vacuum chamber.
The design is to...
Homework Statement
A 25-Ω antenna is connected to a 75-Ω lossless transmission line. Reflections back toward the generator can be eliminated by placing a shunt reactance Z at a distance l from the load (Fig. 1). Determine the values of Z and l.
Homework Equations...
Hello.
Please looks at the attached image first.
The left image is LCC impedance matching network (one of T-type impedance matching networks) and the right is the corresponding equivalent circuit when CT and CL are adjusted such that an equivalent impedance of the sub-circuit surrounded by...
Hello.
Please look at the attached image first.
There are two circuits A and B which have individual electrical components a and b. Components a and b are electrically and directly connected by the red lines. Impedances of individual components a and b are not matched, however, equivalent...
I am measuring a communications bus with an oscilloscope at various points along the line. I understand that there will be reflections at each stub as well as at the ends of the bus if the impedance doesn't match. I also understand that these reflected signals will add/subtract with the...
I'm working out an impedance matching problem from a textbook (it is not part of any coursework) and I am trying to figure out how they get the 315 term in the polar coordinates below.
Z = (XC*RL)/(XC+RL)
= (-j333*(1000))/(-j333+1000)
= 315 , -71.58*
= 100 -j300 ohms
I calculated that...
I've searched high and low for data regarding this from scientific papers to books and I cannot find anything in regards to the approximate impedance to excite a vacuum vessel to plasma state.
In particular I want to built a RF Plasma cleaning chamber, however, I am not sure how to design the...
Homework Statement
https://scontent-lax3-1.xx.fbcdn.net/v/t34.0-12/14804959_10155526179417281_80533891_n.png?oh=649ee14155ac558b21c6553f003e418b&oe=5809EAA0
Homework Equations
The Attempt at a Solution
1) I determined the input impedance of the first transmission line (Zin1).
2) I calculated...
Hello,
I'm confused about the concept of impedance matching in regards with hydrophones and DAQs. If the input impedance to an ADC channel on a DAQ is very high, would I need whatever's being fed into it (hydrophone) to also need a high impedance? Or would it need a low impedance? I've tried...
I am now trying to design a photonic integrated circuit which will be used to replace the global interconnect layer of a LSI. I need to somehow take the output of a photodiode w/o TIA (10G signal perhaps) and then transmit that signal to other layer of the LSI by TSV or something. Assume a...
Hey guys, I am trying to design an Inductive Square Antenna Coil that will be milled onto my PCB. I am slightly confused when it comes to the matching circuit. To my understanding the matching circuit is there to have the same impedance value of the antenna, correct?
So my matching circuit...
Hi everybody.
I am trying to understand the concept of impedance matching and tuning of RF coil.
As far as I understand there are 2 stages:
At the first stage I should match the coil to the source (Let's say with L network method) and the second stage is to tune coil to the desirable frequency...
Hi everybody.
I am trying to understand the concept of impedance matching and tuning of RF coil.
As far as I understand there are 2 stages:
At the first stage I should match the coil to the source (Let's say with L network method) and the second stage is to tune coil to the desirable...
Hello.
I have questions for transmission line and please see the image below.
This is the circuit what I made in which ZO and ZL are output and load impedances, respectively. The commercial voltage probe with oscilloscope is used to measure VL, voltage over ZL . VO, the voltage difference...
Hi,
I'm in a bind trying to determine how to handle impedance matching through a joint of copper wire sandwiched between two 50-ohm coaxial cables (the joint is an interface between atmosphere and a UHV system). There is a signal pulse with a rise time of 2 ns coming through one of the coaxial...
I need to somehow take the output of a CMOS IC and transmit that signal over a 50 Ohm Microstrip line.
The output impedance of the CMOS IC is about 15 megaohms. I see a lot of examples for going from 75 ohms to 50 ohms or similar but nothing on something of this magnitude. Any ideas?
CMOS...
I found a fast solenoid valve lying around (~1ms rise time) so I thought it would be fun to hook up to a compressed air line and use to generate some really loud bass. I hooked it up to a function generator and air supply only to find that it was disappointingly quiet (well not quiet, but...
Hello.
The attached image is L impedance matching network, use for impedance matching between source and load impedance.
The calculation shows that in this circuit, load impedance Rp sees whole impedance (equivalent impedance) of the source impedance and reactive components as matched to...
Hello
I'm now studying transmission line theory. I got to know how impedance matching between characteristic impedance of transmission line and electrical load is important to achieve maximum power transfer and minimize power reflection which causes danger for the system.
But the textbook...
The following show the idea how a Thevenin equivalent source is used to replace the primary circuit of transformer.
https://www.dropbox.com/s/0kaazx1d1srgirz/reflectedsource.jpg?dl=0
https://www.dropbox.com/s/0kaazx1d1srgirz/reflectedsource.jpg?dl=0
In textbook it is commonly stated that the...
Homework Statement
I am calculating matching impedances for a source and its load using 2 different L-network topologies.
One is:
source-parallel-to-C, load-series-to-L
and the other is:
source-parallel-to-L, load-series-to-C.
I go through all the calculations and notice that...
Homework Statement
We need to connect two coax cables with the same dielectric (εr = 9) but
with different dimensions as shown. How big must be the radius of the
outer conductor of the second line in order to match two lines?
How would the velocity of the wave propagation change, if we...
I would like to impedance match a few joints in a circuit and would appreciate some thoughts about this, since I would like the match to be as perfect as possible. The problem is complicated by the fact that the available equipment only consists of trimpot(s). The joints are mostly cables to...
(This is not a question I was given to solve, it is a question about the course notes.)
Homework Statement
In impedance matching, what is the next best method after the complex conjugate method?
If the source has V_s and Z_s, what should Z_L be?
V_s, Z_s, and Z_L are in series.
Homework...
Can anyone help me with impedance matching WITHOUT using smith charts. I am trying to develop a mathcad template to calculate imput impedances for normal power line systems as well as parallel and series impedance matching. I was not very good at using smith charts and never really got the...
Hey all,
Between two devices, I will need to have a coaxial line (with SMA connections on either end) connecting them. The operating frequency of the signal I am propagating is approximately 125 MHz. With this said, the wavelength (assuming ideal) is 2.4 meters.
I have heard from numerous...
Why is so much emphasis placed on matching the impedance of a feed line with an antenna?
Shouldn't the emphasis be placed on matching the internal generator impedance AND feed line with the antenna instead?
That is, you take the impedance of the source, transform it using the transmission...
i have designed my circuit, but i am confused about impedance matching. i know we can use a resistor for matching, but is it possible to use a capacitor or inductor for matching the impedance in a circuit.
In the case of a complex source impedance ZS and load impedance ZL, maximum power transfer is obtained when ZS = ZL*.
For a lossless transmission line terminated on one end with a purely resistive load, zero reflection is obtained when ZS=ZL.
What about the case of a lossy transmission...
Hello everybody,
I've often read that if a light ray travels from a medium 1 to a medium 2 and the two media have the same impedance, there is no reflected light at all, only transmitted light.
So i made some calculations assuming to have two media with two different refractive indexes but same...
Hello,
I wonder if there's any difference between the "impedance matching" and "maximum power transfer" criterion?
I assume in both cases, one impedance should be designed to be the complex conjugate of the other.
Thanks.
I need to make an impedance matching circuit using microstrip lines.
Zin --> MATCHING CIRCUIT --> ZL
The input impedance (Zin) is 50Ω. The impedance at the load is 50 - j 500Ω. Design frequency of 900MHz.
The board I am required to use is the Taconic RF-35. It has a thickness of d = 1.524mm...
I am not sure how the use of a terminator with an oscilloscope works.
I have a signal going into the input of an oscilloscope and improved this signal by attaching a terminator to the input of the scope.
The way I understand it is, that the scope has a large impedance, larger than the...
1. It is required to pass a current of between 6.0A and 6.5A through an impedance of (1.6 + 1.2i) ohms. With only a 230V supply available, it is proposed to use a transformer for impedance matching. A transformer is available with a turns ratio of 16:1. A laboratory test showed that with the...
Homework Statement
A matching network consists of a length of T-line in series with a capacitor. Determine the length(in wavelength) required of the T-line section and the capacitor value needed (at 1 GHz) to match a 10-j35 ohm load impedance to the 50 ohm line