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Q&A

Is this AD8307 fake?

+1
−4

I am trying to test a AD8307. Here are my connections:

AD8307

(pins not shown are left unconnected, and also pin 8).

I get a quiescent output voltage at pin 4 of about 850 mV with respect to ground, which, to my best understanding, means that the IC is fake.

What do you think?

ADDED: As I wrote, pin 8 is left unconnected. According to the datasheet, the input impedance of the IC is 1 kOhm. I am not working inside a microwave oven or near high voltage sparks, so, I can hardly imagine that the tiny pin 8 acts as an antenna or so to provide such a voltage discrepancy, but to make that sure, I tried to put it in a metal box and that made no difference.

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7 comments

What makes you think it is fake in the first place? Did you buy it from the spot market? Lundin‭ 14 days ago

Do you have a "real" AD8307? What is its output at pin 4 for this circuit? Joel Reyes Noche‭ 14 days ago

@Lundin. I don't know what is "spot market", but if that means "Chinese market", then yes. That question is also a way to know if I am understanding right the IC. coquelicot‭ 14 days ago

@Joel Reyes Noche. Yes, I have a real AD8307, and I tried two from the five I've ordered. According to the datasheet (link in the question), output 4 is the "out" pin. coquelicot‭ 14 days ago

@coquelicot‭ It means buying from component traders instead of the usual well-known vendors. There is a huge market of people buying and selling electronic components similar to stock trading. It's the last resort where you go when you can't buy obsolete parts from a trusted source. And it is filled with scammers, cheap illegal copies, silicon dummies and so on. Lundin‭ 13 days ago

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1 answer

+0
−0

I am not familiar with that chip, and only took a very quick look at the datasheet. Here is the block diagram of the part from the top of the first page:

A few things pop out from this:

  1. This chip has a differential input on pins 8 and 1. You tied the negative input to ground via a cap, but left the positive input floating. This leaves open the possibility of the input seeing stray signals, especially considering this chip is intended to work over radio frequencies that are common all around us.
  2. You don't show what you have done with the INT input (pin 5), so we can only assume various strange things. This could clearly cause problems.
  3. You don't show what you have done with OFS (pin 3), so we can only assume various strange things. This could clearly cause problems.
  4. The 850 mV output is across 12.5 kΩ internally. That means 68 µA are coming out of the "MIRROR" block, which implies 34 dB input. How do you know that is incorrect, given the floating input and who knows what connected to the INT and OFS pins?

In summary, given all the strange things you're doing to this chip, we can't tell what its output should be, and can't comment on whether it is working correctly or not. You need to fix your schematic symbol then document your actual circuit properly. Maybe in the process of that you'll find a problem yourself.

Added

I skimmed the datasheet a little further and found this plot:

This shows that if you actually left INT open, then your output voltage indicates about -50 dBm input. How do you know you don't have that? Again, though, since we don't know what you did with the INT pin, anything is possible. I'm going to stop here because speculating further with so much missing information is likely just going to waste my time.

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2 comments

@Olin. Fig 32 ("basic connections suitable for many applications") and fig. 35 for example indicate to leave pin 3 and 5 not connected. It is evident that if I don't show a pin in a schematic, that means it is not connected, as is common in electronics. In a QA site, the criterion for "wasting your time" in an answer should be: "have I clarified things in the mind of the OP?", not the quality of the question itself. If you want to answer only to perfect questions, ask them yourself. thx. coquelicot‭ 14 days ago

@coq: It is not evident at all how pins are connected when not shown. To show an unconnected pin, show it with nothing connected. The quality of a question is always relevant. When volunteering, it is totally the volunteer's call as to what constitutes wasting of time. Olin Lathrop‭ 13 days ago

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