Impedence Matching...

[Lord Loh.]

Although I have use the term "impedence matching" several times in the class as well as on the forum, I regret that I know very littel about it.

What is impedence matching ?
Why do it ?
What if we do not bother about it ?
How do I analyze impedence matching networks ?

Can anyone help me with these questions?
I shall be greatful for any link or explaination or e-text.

Thank You.

 

[nikhil]

hi

impedence matching is to perform to absorb the reflection created by the receiver side. this comes into picture only when the interconnect length between the two gate acts as transmission line as now it is not assume as lumped connection. this will comes into effect only when the electrical length of the rise time is exceed the one-sixth. hence there is distributed effect through the length. so to acheive faithfull signal level u have to match the driver impedence plus characteristics impedence equal to the receiver impedence.

nikhil

 

[Lord Loh.]

this comes into picture only when the interconnect length between the two gate acts as transmission line as now it is not assume as lumped connection.

So does this mean that there is no reason for impedence matching network in low frequency circuit. I understand that radiation occurs effectively only at high frequency. Or when the line is λ/4 or so.

this will comes into effect only when the electrical length of the rise time is exceed the one-sixth. hence there is distributed effect through the length. so to acheive faithfull signal level u have to match the driver impedence plus characteristics impedence equal to the receiver impedence.

Sorry... I do not get this part...one-sixth of what? Is this only for square waves ?

Thank you.

 

[elbadry]

I think that impedance matching is immaterial at low frequencies or more accurately if the line length is less than λ/4. That's why in RFIC impedance matching is only performed at the interface (interface between Rx and antenna or between Tx and Antenna or in general any signal going off-chip at RF frequencies)

That's also why some sort of impedance matching is necessary for telephone lines (these operate at low frequencies but travel long distances)...

 

[homefree]

What is impedence matching:
Use a device, such as transformer or emmiter follower circuit to match output impeadance of the former circuit to input impeadance of next circuit.

Why do it :
According to AC theorem, when the impeadances is matched, the max. power from former circuit will transfer to next circuit.

What if we do not bother about it:
In power circuit, such as audio power amplifier, the output power will be low.
In communication circuit, especially in rf circuit, besides of power loss, it will create more troubles, such as standing wave, echo noise.....

How do I analyze impedence matching networks:
If working frequency below/around audio frequency--
By transformer matching: Z1/Z2=N1^2/N2^2
By cuircuitlease refer to basic electronic book.
If working frequency in rf range--
Please refer to microwave text book.

 

[djalli]

this will comes into effect only when the electrical length of the rise time is exceed the one-sixth.

I must add to this comment that this is ballpark figure and is an agreement, hence standard also, engineers decided to go with. Nothing magical with it. Engineers obey standards. If you wondered where this number/figure comes.

Added after 7 minutes:

If a load(your heater) has same exact conjugate impedance as source: Maximum Power to the load is applied. This is when: source impedance is precisely the conjugate of load impedance.

 

[carrier]

impedance matching commonly use in the high frequency aplifiere design.
you can use the matching for this reson
1-obtain the max of gain
2-minimum the noise
3-transfer the max power to load
4-reflection of eergy is low
and so on. you can use the RF circuit design by Ludwig in the EDA book download for more information

 

[a_ronagh]

hi
The need for matching networks arises because amplifiers, in order to deliver maximum power to a load or to perform in a certain desired way , must be properly terminated at both the input and the output ports.
I have shown you a block diagram of a microwave amplifier in the file that have sent.
for designing microwave amplifiers and impedance matching networks, refer to the "MICROWAVE TRANSISTOR AMPLIFIERS analysis and design" by Guillermo Gonzalez.

 

[freewilly30]

impedence matching is that the load resistance is equal to the output resistance of your circuit...
that ensures maximum power delivery for your load

 

[tuza2000]

is there any picture about impedence matching?
i want to know how to use it.

Added after 1 minutes:

what's the input matching network and output matching network mean in im.doc?
how can we design it?

 

[MRFGUY]

is there any picture about impedence matching?
i want to know how to use it.

Added after 1 minutes:

what's the input matching network and output matching network mean in im.doc?
how can we design it?

matching network in that picture mean matching circuit (that can be LC or stub). This circuit try to match between input impedance and 50ohm at the input side, output impedance and load (50 ohm) at the load side. For LC circuits it only include one series L and one shunt C or one shunt L and one series C. It is easy to find by using smith chart manually or by using software.

 

[djalli]

impedence matching is that the load resistance is equal to the output resistance of your circuit...
that ensures maximum power delivery for your load

If both load(your mean source?) and output resistance are real numbers the answer is YES. In theory and low-frequency this is the case. But this happens in 1% of the cases.

In most of the cases (let say 99% of them) these are not real numbers. Lots of inductance and capacitance is introduced to load/source resistance and in this case: load impedance must be equal to conjugate of source impedance. And if they are not equal your have to match it.

If you do not match it what will happen?
1) Power is not fully delivered. Power is bandwidth, hence what? Client gets for example 80% of he pays. He complains and you are fired as incompetent!

2) Reflection of lost power coming back will be used based on some propability distribution rules as noise in circuit spontaneously without your control of it and you having no control of it.
etc.

So match it!

 

[vale]

impedence matching is that the load
If you do not match it what will happen?
1) Power is not fully delivered. Power is bandwidth, hence what? Client gets for example 80% of he pays. He complains and you are fired as incompetent!

2) Reflection of lost power coming back will be used based on some propability distribution rules as noise in circuit spontaneously without your control of it and you having no control of it.
etc.

So match it!

Hi djalli,
I had same understanding as yours days before, but it is not correct. You may mix up conjugate matching for max power transfer and reflectionless matching for min reflection.
Pls check the chapter of "Electromagnetic Waves and Antennas" (https://www.ece.rutgers.edu/~orfanidi/ewa/)
https://www.ece.rutgers.edu/~orfanidi/ewa/ch11.pdf

 

[pengboy]

I believe it is more related to signal integrity.

basicly, we need to transmitt information, and we dont care about if it is voltage, current signal or power signal.

the matching is used to reduce the mutual reflection. because if the tansmitted information or signal is mingled with delayed reflected information or signal, you will not get a clean or correct information on the recieving terminal. sometime it will totally ruin the signal.

for low frequency, low bandwidth signal, because the effect of the delay is neglegible ( the reflected signal is almost sychronized with the input signal), so reflection does not bring any trouble. that is why for operational amplifier we need very high input impedence and we dont care about matching. and the information is transmitted by voltage signal and we dont care about maximum power transfer.

but for high frequency, your circuit is on the same scale of the wave length of the transmmited signal, we have to consider the effect of delay. and we have to transmite signal using power signals.

in sumary, EM theory is more accurate. the lumped circuit theory is the approximation which neglects the delay effect for low frequency or small circui compared with the wave length.