Stephen Casey wrote: > Hello Rene, > > Indeed I agree with you. The behaviour was that a previously low distortion > (<-90dB THD and IMD) op-amp based circuit, when re-laid out on a new PCB was > displaying distortion at higher than -35dB. Removal of the power rail > decoupling caps fixed the THD, but is not a very ideal solution! The problem > was due to the ground returns for the caps being of too high an impedance, > and the current spikes were injecting garbage into the signal path. I tried > to simulate the behaviour but the macromodels don't show the distortion that > I was getting, so I wanted to see if a transistor level model would work > better for this. It was more of a question of interest than a need to solve > a problem. The problem solution is easy - one plane for cap returns, and one > plane for signal ground, joined at one place. That has fixed it.
You'd probably have to construct models for the power supply and ground environment. Probably a series resistor and inductor, maybe similar components for the lead frame of the chip, too. Jon * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * To post a message: mailto:[EMAIL PROTECTED] * * To leave this list visit: * http://www.techservinc.com/protelusers/leave.html * * Contact the list manager: * mailto:[EMAIL PROTECTED] * * Forum Guidelines Rules: * http://www.techservinc.com/protelusers/forumrules.html * * Browse or Search previous postings: * http://www.mail-archive.com/[email protected] * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
