Communities

Writing
Writing
Codidact Meta
Codidact Meta
The Great Outdoors
The Great Outdoors
Photography & Video
Photography & Video
Scientific Speculation
Scientific Speculation
Cooking
Cooking
Electrical Engineering
Electrical Engineering
Judaism
Judaism
Languages & Linguistics
Languages & Linguistics
Software Development
Software Development
Mathematics
Mathematics
Christianity
Christianity
Code Golf
Code Golf
Music
Music
Physics
Physics
Linux Systems
Linux Systems
Power Users
Power Users

Dashboard
Notifications
Mark all as read
Q&A

Is this AD8307 fake?

+1
−5

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.

Why does this post require moderator attention?
You might want to add some details to your flag.
Why should this post be closed?

1 comment thread

General comments (7 comments)

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.

Why does this post require moderator attention?
You might want to add some details to your flag.

1 comment thread

General comments (2 comments)

Sign up to answer this question »