aaron_do
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Hi baab,
you are designing a receiver, not a transmitter. Traditionally, a power amplifier is found in the transmitter chain. What you need to design is simply an RF amplifier, not a power amplifier (PA).
You are right, a PA might output 10 dBm (10 mW) or more. Anything less than that and it can hardly be called a PA (maybe in some cases). For PA design, efficiency is very important, and it requires you to "design the load". For instance, if your efficiency is 20 %, and your PA is the most power hungry circuit, then you need to burn at least 50 mW from your DC supply. Based on your battery, you can estimate how long your circuit needs between charges (for example, a 1.5 V battery with 1 Ah rating will last 30 hrs ~ 1 day). There are of course a lot of other considerations...I'm just trying to give you an idea.
Your output power is -70 dBm (that's 100 pW). That means it would take 100 million times longer to output the same amount of energy as the 10 mW PA. It absolutely doesn't make any sense at all to talk about efficiency in this case, as even the least power hungry block in your circuit would consume orders or magnitude more power than your amplifier's output power. For a VDD of 1 V, that means your load is 10 GOhm. This is not even close to being close to being practical.
For your design, you have other considerations. As you only have 10 dB gain in front, you will still need to concern yourself with noise. Apart from that, stability will be very important, as a 50 dB gain RF amp is not trivial. In fact, I wonder why you put so much gain at RF? You may still need to have an output matching network, depending on the interface, but your design considerations will be totally different from a PA.
I suggest you try and read up more about receiver/transmitter system design to give yourself a better idea of what you're designing.
regards, Aaron
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