I am designing a broad band 40 dBm power amplifier (PA) in the frequency range of 0.5-2.5 GHz. I would like to implement Automatic Gain Control (AGC) to precisely control the output power of the PA. After much research, I decided to use HMC1120, mainly because from the RMSOUT vs. Pin diagram (as shown below), it appeared to me that HMC1120 offers consistent RMSOUT for my frequency range of 0.5-2.5 GHz and also good sensitivity. (I understand that I need to convert the RMSOUT with something like AD8062 to provide a negative loop for AGC).
When I started looking for variable gain amplifiers (VGA), the ADL5330 appeared to be an attractive choice. However, going through the datasheet, I noticed that the example shown in Figure 37 of the ADL5330 datasheet (shown below) has used AD8318 for detecting the power in AGC.
I started exploring the AD8318 datasheet and noticed that Figures 42 and 43 of the datasheet shows a similar diagram.
AD8318 also appeared to offer consistent Vout for my frequency range but obviously the slope is negative and this will eliminate the need for converting the slope:
More research led into the Figure 44 of the ADL5513 datasheet, which also offers consistent Vout for my frequency range (as shown on page 8 of the data sheet)
So, now I am confused as to which components to use. Here are my questions:
1) Can you please explain which component I should use in my design (HMC1120, AD8318, or ADL5513) and why?
2) As to VGA, can I use ADL5330 to cover the frequency range of 0.5-2.5 GHz? Is there a better choice that I should look into?
3) I am planning to use a directional coupler at the output of the PA, and then connect the coupler (with correct attenuation) to the HMC1120 to monitor output power. In addition, I need to use a gain stage between my PA and ADL5330 to provide sufficient input for my PA. That is, I will have three "stages" or "modules" in my control loop. Would the same control loop --such as the one shown in Figure 42 of the AD8318 datasheet-- work stably in my configuration? (In all examples --such as Figure 42 of the AD8318 datasheet-- the AGC is a single stage.).
Thanks again for your help.