# Will there be a perfect Impedance Matching in general day to day devices circuits

#### Harish G

Joined Oct 21, 2016
34
What I don't get is that how can there be a perfect impedance matching in example: wireless devices.

especially if I consider wireless devices sending the information over a wireless channel.

If a router circuit sends the information and a mobile device receives the information then how does the impedance matching concept works there ?

Note: Consider making no distinction between data and power in this case.

Did someone have an idea on this ?

Thanks.

#### Papabravo

Joined Feb 24, 2006
13,466
I would go back to first principles and ask yourself:
1. What is the purpose of impedance matching?
2. Does it apply to wireless devices separated by some specified distance?
Once you have answered those two questions we will have some context for further discussion.

#### Harish G

Joined Oct 21, 2016
34
I would go back to first principles and ask yourself:
1. What is the purpose of impedance matching?
2. Does it apply to wireless devices separated by some specified distance?
Once you have answered those two questions we will have some context for further discussion.

1. It helps to maximize the power transferred to the load.
2.Yes it applies to wireless devices. In case of wireless energy transfer devices. Sorry I took an example of router. Router may not be used as of now for power transfer, may be in the future.

If someone gives an additional answer to the wireline devices, how does the impedance matching wroks there, how perfect they are in day to day devices. I would take it.

#### AnalogKid

Joined Aug 1, 2013
8,377
First, there never ever is perfect impedance matching. But you can come very close. There is impedance matching:

from the RF amplifier chip to the pc board trace
from the trace to the antenna connector
from the antenna connector to the transmitting antenna
from the antenna to the universe
from the universe to the receiving antenna
from the antenna to the antenna connector
from the antenna connector to the pc board trace
from the pc board trace to the receiver IC

Sometimes the impedance matching is by design, such as a 50 ohm stripline pc board trace matching to a 50 ohm SMA antenna connector. Sometimes the matching is done with a transformer.

ak

#### Harish G

Joined Oct 21, 2016
34
First, there never ever is perfect impedance matching. But you can come very close. There is impedance matching:

from the RF amplifier chip to the pc board trace
from the trace to the antenna connector
from the antenna connector to the transmitting antenna
from the antenna to the universe
from the universe to the receiving antenna
from the antenna to the antenna connector
from the antenna connector to the pc board trace
from the pc board trace to the receiver IC

Sometimes the impedance matching is by design, such as a 50 ohm stripline pc board trace matching to a 50 ohm SMA antenna connector. Sometimes the matching is done with a transformer.

ak
Ok.

Considering I built a device, and I attach different load (again some terminal devices) to it. The impedance matching to occur, the source circuit should sense the change in the load and adapt somehow (I doubt that can be possible) or the terminal device has to match to the source impedance somehow and come close to matching.

#### Papabravo

Joined Feb 24, 2006
13,466

1. It helps to maximize the power transferred to the load.
2.Yes it applies to wireless devices. In case of wireless energy transfer devices. Sorry I took an example of router. Router may not be used as of now for power transfer, may be in the future.

If someone gives an additional answer to the wireline devices, how does the impedance matching wroks there, how perfect they are in day to day devices. I would take it.
Your answer to #1 is only part of the story. In case the power has nowhere else to go except the load you can avoid reflections back to the source and maximize power transfer. The problem is that the match only applies to a single frequency. What you are generally more interested in is how good is the match over a range of frequencies. In the case of radiating RF power from an isotropic source it hardly matters since you can only recover a tiny fraction of that power with even the very best of antennas. Here it is not a question of maximum power, but the recovery of any power at all.

OK so an isotropic radiator is probably not the best power transmitter. Let's try a directional antenna. The problem is that RF won't stay focused; it wants to spread out as the distance increases, and the problem is to recover any power at all from a directed beam.

I don't know what your ultimate aim is but it will be a heavy lift regardless.

#### AnalogKid

Joined Aug 1, 2013
8,377
Considering I built a device, and I attach different load (again some terminal devices) to it. The impedance matching to occur, the source circuit should sense the change in the load and adapt somehow (I doubt that can be possible) or the terminal device has to match to the source impedance somehow and come close to matching.
In standard RF circuit design, that is not how it works. The source does not adjust itself to adapt to changes in the load impedance. Yes, the output voltage and current vary with the load, but not the output impedance. The source has a fixed output impedance, and if the load does not match it then the circuit does not work at its best.

ak

#### Harish G

Joined Oct 21, 2016
34
In standard RF circuit design, that is not how it works. The source does not adjust itself to adapt to changes in the load impedance. Yes, the output voltage and current vary with the load, but not the output impedance. The source has a fixed output impedance, and if the load does not match it then the circuit does not work at its best.

ak
You said "Yes, the output voltage and current vary with the load, but not the output impedance. The source has a fixed output impedance, and if the load does not match it then the circuit does not work at its best."

Yes that is exactly what I want to know. In real scenarios the impedance of the source would be hardly matching to the impedance at the other end. But how can you exploit the use of maximum power transfer theorem there ? its impossible to achieve perfect matching ?

#### Harish G

Joined Oct 21, 2016
34
In standard RF circuit design, that is not how it works. The source does not adjust itself to adapt to changes in the load impedance. Yes, the output voltage and current vary with the load, but not the output impedance. The source has a fixed output impedance, and if the load does not match it then the circuit does not work at its best.

ak

Just read this somewhere "This paper presents a novel serial/parallel capacitor matrix in the transmitter, where the impedance can be automatically reconfigured to track the optimum impedance-matching point in the case of varying distances."

#### AnalogKid

Joined Aug 1, 2013
8,377
"Somewhere" usually means "not here". A circuit designed for one specific application usually cannot be generalized into rules of behavior in other applications. Plus, "automatically reconfigured" might mean motor-driven capacitor connectors.

I'm not sure what you are trying to achieve with this line of questioning. MPTT is a statement about the consequences of a relationship. It is not a hard and fast design rule. It describes the conditions when one particular aspect of a circuit's function is at a peak condition. Since perfect impedance matching is almost impossible, MPTT is a design goal for some applications, not a universal rule. For example, in DC power supply applications, the conditions of MPTT are almost never met.

ak

#### Harish G

Joined Oct 21, 2016
34
"Somewhere" usually means "not here". A circuit designed for one specific application usually cannot be generalized into rules of behavior in other applications. Plus, "automatically reconfigured" might mean motor-driven capacitor connectors.

I'm not sure what you are trying to achieve with this line of questioning. MPTT is a statement about the consequences of a relationship. It is not a hard and fast design rule. It describes the conditions when one particular aspect of a circuit's function is at a peak condition. Since perfect impedance matching is almost impossible, MPTT is a design goal for some applications, not a universal rule. For example, in DC power supply applications, the conditions of MPTT are almost never met.

ak

You said "For example, in DC power supply applications, the conditions of MPTT are almost never met."

Yeah that is what's bugging me, in case of highly energy sensitive networks such as Mutual Inductance networks, it becomes a huge problem.

I think to understand further I need to do my own homework, anyway thanks for the hindsight.