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Design >> Mixed-Signal Design >> measures for substrate noise reduction
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Message started by ywguo on Apr 11^th, 2004, 7:51am

Title: measures for substrate noise reduction
Post by ywguo on Apr 11^th, 2004, 7:51am

Hello,

As well known, substrate noise is a very severe problem in mixed signal circuit design.

Basically, the digital supply and analog supply are seperated on chip. Some papers has presented that guard ring is not effective for low-ohmic substrate. Somebody recommends that analog ground should not connect to substrate because the low-ohmic substrate is polluted by digital circuits.

But I am confused by a practical configuration. It is shown in the following.
vdda 3.3V DAC supply
vssa clean vssa (not connected to substrate), connect to board analog ground
gnda Ground input (connected to substrate), connect to vssa if using high-ohmic substrate, connect to digital gnd! if using low-ohmic substrate.
gnd! substrate ground, keep minimal resistance to gnd! bondpad
vdd! digital supply

Who could explain the configuratoin for me? Thanks very much in advance.

Best Regards,

Yawei Guo