Question I have bought AD9243 evaluation board and i would like to have some pieces of information about grounding; i've seen there are 5 sets of pads and a jumper to connet analog ground and digital ground of PCB; besides, i seem that the pads below ADC's IC are connected. Now, am i supposed to connect the other set of pads to one another as well? Last but not least, am i supposed to connect the AGND and DGND outputs respectively to the analog and digital grounds of the whole system, or need i connect AGND and DGND together to the analog ground of the whole system? Answer It is a common mistake to assume that the DGND pin on an IC is an instruction to connect this pin to the digital ground plane of your system. This is DEFINITELY NOT the case. The pin marked DGND on an IC is intended to let the system designer know that this is where the return current for the digital circuitry on this IC comes out. It's then up to the system designer to decide how to route this current back to it's source. Some thing which you definitely do not want to do is connect this pin (which is after all connected to the same substrate as you precision converter) to a ground plane dedicated to a noisy digital ground plane which is dedicated to the return of fast switching, high current digital circuitry. PCB ground planes do not have zero impedance, and at high frequency they start to look inductive, fast current pulses through an inductor causes large potential differences. Most digital circuitry does not care about these potential differences in the ground plane because of the inherent high noise margin in digital circuits. But, your 12,14 or 16 bit precision converter requires that the potential difference between it's AGND and DGND pins is zero…. always and especially during a conversion. I recommend that you connect AGND and DGND together directly at the ADC. Treat this node as an analog return path and route it separately over a wide ground plane back to the power supply. Do the same for any other ADCs you have in the system, connect AGND and DGND together directly at the IC and route it separately back to the power supply. This will mean that you have separate ground return paths for each ADC. The final chapter in all our seminar books is dedicated to hardware design techniques and deals with such issues as grounding, decoupling, parasitic thermocouples and good PCB design. http://www.analog.com/support/standard_linear/seminar_material/index.html

AD9243: FAQ - Documents - Precision ADCs

Products Mentioned

AD9243 Production
The AD9243 is a 3 MSPS, single supply, 14-bit analog-to- digital converter (ADC). It combines a low cost, high speed CMOS process and a novel architecture...
Datasheet
AD9243 on Analog.com

TOOLS-MISC Obsolete
The Link Port Cable allows you to link an EZ-KIT Lite to another EZ-KIT Lite.
TOOLS-MISC on Analog.com

AD9243: FAQ