Need help on the evaluation board of a capacitive readout chip

[Chengjun Li]

Hi,
I recently bought a capacitive sensor readout from a Japanese company.
They sent me an evaluation board diagram like following,


I magnified the part in the red box.


The corresponding evaluation board picture is as follows.

The lower right corner corresponds to the part in the red box of the diagram.

My question is in the red box, there is a FG, I think it means floating ground. I don't know why there are two ground ( GND and FG) , and they can be connected through a jumper. In what situation should I put on the jumper?


Thanks.

 

[Martaine2005]

I have no idea and couldn't find anything with a quick search..
Have you checked with your DMM whether it makes any difference with and without jumper?
A simple continuity check would verify either way..

Martin

 

[Chengjun Li]

I have no idea and couldn't find anything with a quick search..
Have you checked with your DMM whether it makes any difference with and without jumper?
A simple continuity check would verify either way..

Martin

Actually this evaluation board is no more fabricated several years ago. What I have now is just a picture and diagram. I am trying to build an evaluation board by myself.

 

[Martaine2005]

Yes, sorry. You did say diagram!...
Sorry I cannot help you.

Martin

 

[dorke]

FG is Frame Ground ,also called chassis ground.

It is used in analog or mixed analog/digital circuits to prevent noise interfering with the circuit,
and EMI/RFI suppression in/out of the circuit.

What is this circuit doing?

 

[Chengjun Li]

FG is Frame Ground ,also called chassis ground.

It is used in analog or mixed analog/digital circuits to prevent noise interfering with the circuit,
and EMI/RFI suppression in/out of the circuit.

What is this circuit doing?

This circuit is to measure the tiny capacitance difference between two capacitor with very high accuracy,and typically on the fF scale.
As you said, in order to reduce noise, I should always put a jumper to connect the ground with Frame ground?

 

[AnalogKid]

Or Field Ground. Frame, Field, or Chassis grounds usually are tied to earth ground. This can be at a different potential than the system or signal ground, and this can cause ground loops that inject noise into signal lines and cause other squirrely behavior. There is a jumper so the user has a connect/disconnect option.

ak