I think I've told you before, your spec of -100 dBm output power is very unlikely. Its way too low.

For a first pass approximation, you can calculate the load based on the output power and the supply voltage. i.e. P = V_DD²/(2R_load). I'm assuming single ended and your pk-pk output is 2V_DD. Then you need to size your device to get the required gain based on the load.

After you have your first pass approximation, you can start looking at load-pull, and all of your parasitics, and optimizing for efficiency, linearity etc.


regards,
Aaron

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

Hi,


an RF amplifier is just an amplifier that works at RF. A power amplifier is just an amplifier that amplifies power, and it is usually designed to output a certain maximum power which is quite large.

Why do you need a certain minimum input power for your mixer? Isn't it linear?


regards,
Aaron

Hi,


The RF Power Amplifier must amplify power. An RF Amplifier could amplify either power or voltage depending on the output interface. Usually in an SoC, it amplifies some of both. For a discrete design with 50-ohm input and output, it of course only amplifies power. When you get some experience designing it, you will understand it. One key difference is that as I mentioned before, a PA is usually required to output a lot of power efficiently. For a generic RF Amp, efficiency may not be important.

For the mixer, as far as I know, there isn't usually a minimum input power (except for noise limitations). The thing is, you haven't revealed anything about what technology you're using, or what is your operating frequency, so I don't know if you're working under limitations...

Quote:


Nope. When you said your mixer requires a certain input power, I assumed you meant it wouldn't work below that power. That means either its NF is really bad, or its non-linear.


Aaron

Hi baab,


the purpose of the 10 Gohm impedance is to get good efficiency in your PA as it will allow you to maximize your output swing for the given output power. If you don't need good efficiency, then you don't need 10 Gohm. In your case, you don't need good efficiency...Besides, if your load was really 10 Gohm, the gain of your amplifier would be tremendous. Practically speaking you will probably end up transforming your 50-ohm load to between 100 ohm and 1 kohm (just a very rough figure).

It is not possible to design an on-chip matching network to transform 50ohm to 10Gohm. You can try and work out the component values and the component Q you would need for an L-match. You would need a component Q on the order of 150,000 (practical Q might be less than 10), and an inductor size on the order of tens of microhenries (practical L might be less than 10 nH). And anyway such an inductor would never be able to work up to 1.7 GHz. I suggest you read up on L-matching, and if you can see what are the practical inductance sizes and Q you can get.


regards,
Aaron

Quote:

Hi,

I want to ask for help again. Please confirm if my understanding is correct.

+ First, I need to calculate load resistance based on the formula:
P = VDD2/(2Rload)

For example, with my specifications VDD = 1V and Pout = -70dBm
=> Rload = 10G ohms.
After got the load resistance, put it into the circuit and do the next step.
+ With the load calculated above, put it into the circuit and sizing the component to get the output power.
And what is the best way to get sizes of components? I know that we need to base on formula but what is needed beyond that?

Thank you, tm123.
Quote:

Yes, but I only has to design RF power amplifier.
Quote:

Yes, of course. I attached it below.
Quote:

Here is my specification:

+ output power: -70dBm
+ power gain: 50dB
+ input/output impedance: 50 ohms.
+ noise figure: not so important but there is no specific number.
+ linearity (IP3, IP2): I didn't get that. I was supposed to determine that myself.

PS. The image attached is in the paper called "Reconfigurable and Simultaneous Dual Band Galileo/GPS Front-end Receiver in 0.13µm RFCMOS ".
I wanted to attach it but it seems impossible here.