Impedance mismatch
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Impedance mismatch is a term in systems analysis which describes an inadequate or excessive ability of one system to accommodate input from another. Although the term originated in the field of electrical engineering, it has been generalized and used as a term of art in systems analysis, electronics, computer science, informatics, and physics.
"Impedance mismatch" is derived from the usage of impedance as a measurement of the ability of one system to efficiently accommodate the output (energy, information, etc.) of another. It is used and measured in many ways, but in general the most efficient exchanges between different systems happen when their impedances are closely matched.
Often the attributes of each system’s interface are cast in the laws of physics and are immutable. We must accept them and do our best to work around them. Other system interfaces while perhaps appearing rigid may in fact be adjustable. So these types of systems can usually be modified allowing them to directly couple with others (so avoiding linking them through some sort of less efficient conversion device or process).
On one end of the spectrum, Impedance mismatch labels a common problem in electrical engineering that occurs when two transmission lines or circuits with different impedances are connected. This can cause signal reflection resulting in attenuation and noise. See also impedance matching.
However, the term is even used to refer to the difficulties encountered when attempting to connect two systems which have very different conceptual bases. The typical example is the Object-Relational impedance mismatch, which occurs when trying to use a relational database management system from an object-oriented program.
Here are some other common examples where the effects of impedance are evident:
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[edit] Mechanical – the automobile transmission
An automobile transmission’s sole purpose is to better match the engine’s output to the changing demands of the road. It is a necessary accommodation we make that addresses the variable torque output of the internal combustion engine to be suitable to the challenges of accelerating a vehicle. To match the system impedances, the driver or the transmission itself adjusts the gear ratio to deliver the best overall efficiency and performance under constantly changing conditions. Interestingly, in the early days of the automobile, steam powered cars were very popular. They did not have or require transmissions as the steam engine impedance was a much better natural fit to the application.
[edit] Electrical – the transmitter antenna
A radio transmitter must use a tuned antenna to enable it to efficiently radiate its output into the surrounding airspace. Without the right length of antenna for the operating frequency, most of the energy will not make it out. So to be efficient the antenna’s properties must be adjusted to match the impedance of electromagnetic propagation through free space.
[edit] Human/human communication - language
If you only speak and understand English and you wish to communicate with someone who only speaks and understands French there will be little information exchanged unless you find a way to match impedances. Your only solution is to employ the services of a translator to convert and bridge your communications. While you have not been prevented from communicating, this approach is much less efficient and much more expensive than communicating in a common language.
[edit] Human/machine communication - language
All computer based systems are built up in layers of function. At the foundation is binary machine code. However, people do not easily or naturally communicate in machine code. To deal with this impedance mismatch, we have transferred much of the translation effort to the machines. Layers of machine software continue to be developed to make the appropriate interface translations more natural and efficient for us. This slows the machines down, but we are happy with the arrangement.
As pointed out by these everyday examples, we see that direct matched couplings are always better (more efficient, less costly, etc.) than relying upon some intermediary conversion/linking device or technique. However, if accommodations must be made, it is better for us when our technology makes them.
[edit] Impedance - human and otherwise
When we speak of impedance mismatch during a discussion of our information infrastructure we are referring to how efficiently and naturally coupled our systems are to each other as well as to us.
Both people and computers can be flexible and adapted to the requirements of some challenge before them, but here we are interested in pointing out how each one is intrinsically wired or set-up.
[edit] Computer impedance
Digital computer based systems run on binary code. Information represented as bits set to represent either one or zero operates on untold numbers of simple logical elements to produce complex and useful work.
However, since many families of microprocessors have been developed and deployed there are several lines of incompatible low level syntaxes and instructions sets. (Think of these as incompatible grammar and vocabulary.)
Fortunately, many layers of code have been developed and applied to allow low level compatibility issues to be masked through translation. While native, common binary instruction sets are the most efficient, the power of today’s systems is so great that translation and interface demanded between incompatible systems is of little consequence.
Therefore, for all intents and purposes any microprocessor based system can be made to emulate or behave as any other. So they can efficiently communicate among themselves in essentially their natural languages.
The Object-Relational impedance mismatch is a philosophical difference that exists between object-oriented programming and the Relational Model in database technology.
[edit] Human impedance
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Human based systems run on who knows what. But it certainly isn’t binary code.
Human beings are sentient and operate via associative memory. Thoughts are triggered and cascaded by association. This is why many of us “go off on a tangent” when engaged in a conversation - one thought is linked via an association with something else, perhaps totally disconnected and unrelated.
To us words and phrases mean things, triggering us to evaluate them in context. To computers, words are no more than data to be manipulated – data without meaning to be acted upon without interpretation.
Further, while admitting to our fair share of incompatible syntaxes, grammars and vocabularies, as a community, we do enjoy a fluency in far richer language structures.
Unlike computers, humans by nature:
- Are sentient.
- Need to set up and follow processes.
- Have an associative memory that drives our thought processes.
- Are apparently wired to organize and classify anything we bump into.
- Naturally “jump around” when we think or navigate through information.
- Communicate in high level languages, far removed from machine code.
- Tolerate ambiguity - can still act with uncertain or incomplete information.
- Are reluctant to assume the burden of translation between ourselves, let alone between us and some machine.
