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As far as I know the RF amplifiers are voltage amplifiers. On the other hand, from transmitter to the receiver there is a lot of effort for impedance matching. But impedance matching aims max power transfer at the load/receiver not the max voltage.

Shouldnt the aim be maximum voltage instead of max power at the recevier amplifer’s input?

Where am I thinking wrong here?

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  • \$\begingroup\$ Don't you want to get the most power for your voltage? \$\endgroup\$ – immibis Sep 12 '18 at 23:16
  • \$\begingroup\$ We want the output impedance to be low to deliver more voltage at an opamp input not the power. We want the voltage divider effect of the output impedance minimium to make the volage max. But in this case we want power max. Not the voltage. That is the confusing part. \$\endgroup\$ – user16307 Sep 12 '18 at 23:21
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Your premise is wrong: RF amplifiers are power amplifiers, and there's impedance matching at every stage in the process. You can always trade off voltage for current by making an impedance transformation, so the key parameter is signal power at the receiver.

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  • \$\begingroup\$ If it is an AM or FM radio for instance, will that max power be converted to max voltage at the audio stage? I mean why is impedance transformation necessary? \$\endgroup\$ – user16307 Sep 12 '18 at 23:12
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The whole point of a transmitter is to increase the power being generated so it may be (1) transmitted to the antenna, and then (2) transmitted to free space by the antenna. You can think of the antenna as an impedance matcher to free space.

So, all along the way you want impedances to match. Otherwise, you end up with power being reflected back to the amplifier stage (and standing waves), rather than maximizing the amount of electromagnetic signal being transmitted through space.

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In implementing RF circuits on silicon, with 10 microns between gain blocks, etc, there is no need for matching, no need to achieve best power transfer, because the useful design mindset is to view the silicon system as a chain of voltage amplifiers.

These circuits may be viewed as very broadband opamps or diff-pairs, etc, instead of narrow-band circuits needing optimal signal energy use.

Also on chip, inductors can be a huge bother.

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