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Impedance matching is one of the major application of common collector configuration. Is Common Collector configuration the best method for impedance matching? why?

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  • \$\begingroup\$ +1 for good question! I eager to see a good answer. \$\endgroup\$ – Roh Feb 28 '14 at 8:01
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    \$\begingroup\$ You can't ask for 'the best' without specifying your context and criteria. A CCC is a good solution when you have a high source impedance, a low required output impedance, a transformer is not a good option, you can live with ~1 voltage amplification, etc. \$\endgroup\$ – Wouter van Ooijen Feb 28 '14 at 11:05
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Impedance matching is NOT one of the major applications of a common collector circuit. Why should a transistor be able to match an impedance? Impedance matching is done with passive components.

A common-collector circuit is good at providing a high input impedance (to a weak signal) and generating a low output impedance (at the emitter) - it is a power amplifier not an impedance matcher.

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    \$\begingroup\$ You're taking the phrase "impedance matching" too literally. Think of it more as a general impedance transformation. Common-collector (emitter follower) matches a high-impedance source to a low-impedance load (unity voltage gain). Common-base matches a low-impedance source to a high-impedance load (unity current gain). Common-emitter is used for intermediate impedances (can have both voltage and current gain). \$\endgroup\$ – Dave Tweed Feb 28 '14 at 13:13
  • \$\begingroup\$ @DaveTweed "Making one impedance equal to another" is what the tag for impedance matching says. \$\endgroup\$ – Andy aka Feb 28 '14 at 13:26
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See let us take an example for a basic analog circuit where the voice signal is amplified and sent to the loudspeaker.

Now your voice signal is not a electrical signal so to process it we require a transducer which give the electrical equivalent of your voice signal. Let the output impedance of the transducer be 100k (assume). Say we connect a CC (common collector) amplifier in the next stage.

As the input impedance of the CC amplifier is very high so the combination of its input impedace and the transducer output impedance will be equal to the transducer output impedance only (Parallel combination ). Hence the CC amplifier doesnt create any loading effect for the transducer output stage.

Now consider the output of CC amplifier . The input impedance of the output device say a loudspeaker is low which matches with the low output impedance of the CC amplifier . Now there is a condition by Maximum Power Transfer Theorem that if the load impedance is same as the circuit impedance the maximum power transfer will take place . Hence the CC transfers maximum power to the output , which is also known as impedance matching.

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