I want to use ADL 5511 to do envelope detection, how to use the chip with its evaluation board?
Especially, how to connect the board into the circuit? It has two SMA interfaces at the RFIN and VENV.
I'm not quite sure of the question. The eval board is intended for lab evaluation. So normally, you connect the board to RF test equipment using SMA cables. Would it make more sense for you to order loose samples and build your own pcb?
The input signal is a beat signal combining two signals, which are 2 GHz and 2.01 GHz. So the envelope profile should be at the frequency of 10 MHz. What I what to do is to detect the envelope of the beating signal. Just like the graph below.
But now the VENV output of the evaluation board is not the envelope of signal. I apply a voltage of 5 V onto the VPOS and GND. Do I need to connect the other pins on the board?
With VPOS and GND connected, check to see if you have the right current, around 21 mA with no RF applied and around 43 ma with full RF input power. If you are seeing no current flowing, check the position of SW1. Try applying a few single tone input powers at 2 GHz and see if you are seeing the correct dc output voltages on VRMS and VENV.
I have checked the current as you said. Both the voltage and current is right.
The output of the VENV is directly connected to the oscilloscope, but there is no envelope, only a flat line. And the flat line is related to the voltage applied. The more voltage applied, the higher the flat line is.
Can you upload a scope photo. One thing I noticed in the photo you provided of the eval board is that you have the two black wires connected to VRMS and EREF, not to VENV and EREF. Also, the input impedance of the scope should be set to High.
The other two black cables don't connect to anything.
Understood. So you are applying power via the red and black cables on the top and have VENV connected to the scope using an SMA cable or scope probe with the scope input set to high input impedance?
Yes, but no envelop seen in the scope. Is there anything else I missed when operating this ADL 5511?
I'll take a quick look in the lab to see if there is something we are missing. So to be clear, you have not made any changes to the eval board, that is, adding or removing components, right? If your input frequency is around 2 GHz, no modifications should be required.
Yes, I didn't make any changes. Thank you.
Here is a plot of what I saw when I repeated your setup. I set the two input tones to around -10 dBm, one at 2 GHz and one at 2.01 GHz. I'm seeing the expected beat frequency sitting on top of a large dc voltage (this output has a baseline offset of 1.1 V). If I change the input impedance of the scope to 50 ohms, the beat frequency disappears because the output cannot drive the load. Also, you should check in case one of your signal generators is not working. If you turn off Sig Gen A, the output from ADL5511 will revert to dc but will go up and down as you vary the input power on Sig Gen B and vice versa.
Other than that, I'm not sure what could be causing you to only see dc on the output.
Thank you very much. It works now. It was because the scope impedance.
One more thing, is there any way to make the board be able to drive the device with 50 ohm input impedance? Or is there any other envelope detector could operate with the device with 50 ohm input impedance? Thank you.
Your safest bet is to use an rail-to-rail op-amp such as AD8031 (there are probably newer options but I'm familiar with this one). You will need to configure the op-amp as a differential amplifier so that you can strip of the 1.1 V dc bias level that the output sits on. Alternatively, you could ac-couple into your 50 ohm load.
Another device to consider is ADL6010. It has almost enough output current to drive a 50 ohm load and its output is referenced to ground.
I think I prefer the first method, adding an op-amp after. For the op-amp, I find that the evaluation board has a lot of resisters and capacitors that is user defined. Is there any information about what specific values should I choose?
This is the set up and the scope screen.
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