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Design >> Mixed-Signal Design >> Substrate connection in a pipelined ADC
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Message started by Stan on Jun 13^th, 2005, 6:41pm

Title: Substrate connection in a pipelined ADC
Post by Stan on Jun 13^th, 2005, 6:41pm

Hi,

Where should I connect the substrate in a pipelined ADC? To the analog ground or the digital ground? I have checked several books but got inconsistent answers.
Thank you!

Stan

Title: Re: Substrate connection in a pipelined ADC
Post by sheldon on Jun 21^st, 2005, 9:10pm

Stan,

First it would help to know more about the application? Are you
putting the ADC in the middle of 1,000,000 noisy gates? Or is it
standalone? Also why does your Pipeline ADC macro have only one
ground? Wouldn't it be better to separate the grounds into analog and
digital to prevent crosstalk? Does all your digital logic run off the
same supplies as the analog or is there high and low voltage digital,
that is do you need three ground lines analog, high voltage digital,
and low voltage digital? When the design was simulated was it simulated
with package parasitics? If not probably need to do this simulation to
understand how to partition the power supllies.

Best Regards,

Sheldon

Title: Re: Substrate connection in a pipelined ADC
Post by sheldon on Jun 21^st, 2005, 9:18pm

Stan,

Sorry got off the topic, it depends on a lot of factors. In general, the
answer is neither, give it an isolated supply to an isolated pin with
really low impedance to ground. The goal is to minimize noise
injection from the subtrate by shorting the local substrate to ground.

Sheldon