I want to buy ADA4530 eval board but i have a doubt in the layers in pcb layout. there are 4 layers in this design , but there i am unable to find the common connection between the power supply ground and signal ground , i.e the point of connection between the two layers i am missing . can you please help me with this doubt.
the 4 layer picture i am attaching
I think blue layer you have is covering up the resistor/jumper positions in the green layer that would connect the power ground with the analog ground.
Could you change the layers to have green on top? I think that would give a better idea of where the connection is.
Not seeing what’s going on on the green layer these two areas look like suspects for ground connections.
those points(which you had highlighted) are there to connect top layer and second layer ground connections ,i.e signal grounds are connected …but the power supply ground which is indicated as GND in this picture is not connected in any of the 4 layer .The GND is the main power supply ground but that connection to the other layers i am missing .can you please help me with this .
the main power supply GND have to connect to these grounds right? can you help with connection …
Now that I take another look at this design I think the only purpose for that power supply ground is to give those two tantalum capacitors something to connect to to filter the +/- input voltages. Otherwise I don’t think connection to signal ground is needed.
these small holes are connecting 1st layer and 3rd layer . why are the holes there ? what is the purpose of that hole or vias? are they ground vias?
Not sure the purpose of those vias. Potentially those could be anchor points to tie the layers together physically to prevent delamination.
I don’t think that individual box is ground or intended to be ground. I think it is intended to float so it doesn’t get electromagnetically coupled to the layer that is physically attached to the shield.
I believe that rectangular box is keeping the shield box on an adjacent layer from crosstalking into the power ground and the signal ground layers. I say this because I’m assuming the only place they want that shield to be connected to ground is through the coaxial connector on the left.
There is potential that there are vias I cannot see that connect it to the shield box on another layer but I think it might just be sitting there floating. I could be wrong about this.
Hi deepthia,
I would recommend you read the ADA4530-1R-EBZ user’s guide, pages 42-43 of the ADA4530-1ARZ datasheet, and the AN-1373: ADA4530-1 Femtoampere Level Input Bias Current Measurement application note?
These documents give an idea of the thought that goes into the design of the circuit boards in order to take advantage of the exceptional characteristics of the ADA4530. Of key significance is the inclusion of an integrated “guard buffer” within the ADA4530, which is brought out of the chip on pins 2 and 7. Using these pins, the boards are designed to create a guard ring around the input signals and a guard plane to perform ESD shielding. Therefore, the shielding and guard plane are connected to the guard buffer of the chip rather than the power ground and intentionally isolated from the power ground.
i have a doubt regarding the shields connections . the shields which are connected to copper plating in rectangular shape ,are they connected to signal ground or else shields are simply unconnected … can you please clarify the doubt , for what the shields connected to ?
If I’m understanding David correctly, the shield is intentionally not connected to ground, in order to take advantage of the features of the chip. According to page 3 of the user guide, the traces for the shields are electrically connected to amplifier guard potential. That is to say, pins 2 and 7 of the on-board ADA4530-1. They are intentionally not connected to GND.
