SeanGerard
New Member
Hi, I have a question about impedance matching. Excuse my laziness; I could probably figure this out, but I was wondering if anyone knew the answer off-hand.
When you are trying to deliver power from a source, say, Rs = 200 Ohms, and Rl = 50 Ohms, you can match at a particular frequency to obtain maximum power transfer. I get this.
What I don't understand, is, for example, why you impedance match from a source, say Rs 200 Ohms, to the impedance seen between the base and emitter (or 'Re', if there is emitter feedback etc.) of a common emitter amplifier. Since a BJT is essentially a current controlled device, why are you trying to deliver maximum power to it? Does delivering maximum power at the 'input' of a single BJT stage guarantee maximum power at the output? I would think you'd want to maximize Ib, or something like that.
Hopefully this is clear.
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Ok, I get it now, somewhat. I wrote the above about an hour ago, and haven't submitted it yet. It turns out that delivering maximum power to the input does guarantee maximum power gain as long as the output is matched as well. I think I still need to think about this more, so I'll post it anyway, haha. Happy New Year.
When you are trying to deliver power from a source, say, Rs = 200 Ohms, and Rl = 50 Ohms, you can match at a particular frequency to obtain maximum power transfer. I get this.
What I don't understand, is, for example, why you impedance match from a source, say Rs 200 Ohms, to the impedance seen between the base and emitter (or 'Re', if there is emitter feedback etc.) of a common emitter amplifier. Since a BJT is essentially a current controlled device, why are you trying to deliver maximum power to it? Does delivering maximum power at the 'input' of a single BJT stage guarantee maximum power at the output? I would think you'd want to maximize Ib, or something like that.
Hopefully this is clear.
Ok, I get it now, somewhat. I wrote the above about an hour ago, and haven't submitted it yet. It turns out that delivering maximum power to the input does guarantee maximum power gain as long as the output is matched as well. I think I still need to think about this more, so I'll post it anyway, haha. Happy New Year.