impredance matching

[msmukund2000]

please help me on this one...
WHY IS IMPEDANCE MATCHING NECESSARY
thanks ppl..
Bye

 

[Nigel Goodwin]

please help me on this one...
WHY IS IMPEDANCE MATCHING NECESSARY
thanks ppl..
Bye

In regard to what?.

Basically impedance matching is for giving maximum POWER transfer, this may, or may not, be a good thing!. But it varies depending on your application.

 

[Spectacular Butter]

how do i know the input or output impedance of a circuit?

 

[Nigel Goodwin]

how do i know the input or output impedance of a circuit?

You can measure it if you want, but again it all depends on the application, mostly you DON'T want matched impedances in electronics.

 

[msmukund2000]

ur answer is almost what i wanted, iwanted to know why it was used...
btw,i read it in the cfontext of op-amps.
can u explain on it plz,,how does it maximise power transfer??

 

[Spectacular Butter]

You can measure it if you want, but again it all depends on the application, mostly you DON'T want matched impedances in electronics.

Huh why is it that you don't want matched impedance in electronics? won't it save power by using all instead of dissipating as heat?

 

[msmukund2000]

i dont think so,the load may be a low power device, yet again,i think that impedance matching increases the output current also.(Mr.Nigel,could u correct me on that, if i am wrong),so with low current or low power loads,u dont want impedence matching??

 

[msmukund2000]

this sld help

Butter,,on second thoughts, forget all that i said and read the link,i found it useful
https://www.electro-tech-online.com/custompdfs/2004/12/impmatch.pdf

 

[TheOne]

Impedance matching depends very much on the situation.

Examples of where you want matching:
a) Antenna to input or output of RX or TX
b) Driving transducers
c) Microphone pre-amps
d) Filters-crystal etc.

Examples where you don't sometimes:
a) RF input amplifier where you mis-match for low noise rather than max gain
b) RF amplifier where you need stability to prevent it turning into an oscillator :lol:
c) Oscillators, where you want good match of input and output impedances at the required frequency but high losses at the unwanted frequencies

These are just a few, but there will be plenty in various applications

 

[Nigel Goodwin]

You can measure it if you want, but again it all depends on the application, mostly you DON'T want matched impedances in electronics.

Huh why is it that you don't want matched impedance in electronics? won't it save power by using all instead of dissipating as heat?

If you match the impedances you waste 50% of the power in the source (a simple potential divider, with two equal values), but you are transferring the maximum power possible from the source.

Generally in electronics you are looking for voltage transfer, not power transfer - so if you have a 600 ohm microphone, which outputs 5mV, and you connect it to a 600 ohm input impedance, your microphone output drops to 2.5mV. So you've already wasted half of your signal!. If you use a higher input impedance you don't get this loss, generally you'd use something like ten times the source impedance.

Likewise with CD players and amplifier, a CD player probably has an output of 600 ohms to a couple of kilo-ohms. The amplifer it feeds has an input impedance of about 50,000 ohms.

With a transistor amplifer feeding a speaker the speaker is probably 8 ohms, and the amplifier output impedance will be less than 0.1 ohm or so.

Don't forget, an amplifer doesn't amplify the original signal - it simply creates a larger replica of the original signal. So all you need is sufficient input to control the duplication process - you don't need any power to the input.

 

[msmukund2000]

so if impedance matching is so selectively used, then why does an op-amp have an inbuilt impedance matching CCA? does it mean that op-amp's prospects of use are limited by this?

 

[Nigel Goodwin]

so if impedance matching is so selectively used, then why does an op-amp have an inbuilt impedance matching CCA? does it mean that op-amp's prospects of use are limited by this?

Op-amps don't generally have inbuilt impedance matching, a 'perfect' opamp has infinite input impedance, zero output impedance, and infinite gain - the calculations used rely on this, it lets you ignore the opamp in the calculations. Obviously this isn't possible in practice, but they get close enough for the theory to work.

Do you have a specific use in mind for impedance matching?.

 

[msmukund2000]

hi,
thx for replying,
actually , i was being taught abt op-amps at college, when my Lect told me that it has 4 stages, first two being Diff Amps the third being an impedance matching ckt and the fourth, a level shifter...
and gave some explanation for the impedance matching unit ,which i cudnot understand and could not accept ( he said that impedance mismatch could cause more current 2b drawn by the load,which a CEA cannot provide(of course) and so we impedance match
so i set out on a meaning hunt...
now tell me, does the op-amp have Imp Matcher, or not?
and if u have any other comment about the above mentioned str of op-amp,tell me,i am all ears,

and is there anything important i must know abt op-amp,
I WANTED TO USE IT AS A COMPARATOR FOR A LINE FOLLOWER..
so i wanted to know more abt it
Thx