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Keith Sabine

Layout-Dependent Effects in Analog Design

Keith Sabine
fasmicro
fasmicro
11/8/2014 10:44:07 AM
User Rank
Master
Re: Layout is vital
>> @fasmicro: Well it's a precautionary step isn't it ? Do you think by doing this we can mitigate the risk ?

Yes, you can mitigate the risk. The problem in layout is to think that "marketing features" like autorouting can give a decent work. Those features are there so that you do not complain and ask about them when the marketer comes to sell things.

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uchiha
uchiha
11/4/2014 8:41:24 AM
User Rank
Artist
Re: Layout is vital
@fasmicro: Well it's a precautionary step isn't it ? Do you think by doing this we can mitigate the risk ?

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fasmicro
fasmicro
11/3/2014 7:04:50 PM
User Rank
Master
Re: Layout is vital
>> While traditionally people did route critical nets first, and sometimes finish the routing of non-critical nets automatically, the problem with this approach is that you need a good placement as a starting point.

The reverse is a better strategy - Start by routing critical nets manually and then autoroute the non-critical ones. I have used Protel and you can set such that it cannot change already routed nets. In digital VLSI, you can also do same with many of the tools in the market. Route critical nets manually and finish with autorouting.

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fasmicro
fasmicro
11/3/2014 6:59:16 PM
User Rank
Master
Re: Layout is vital
>> More companies have become chip design firms over fab based providers to reduce capital costs.

That is the core of TSMC's strategy. No many companies can wake up and invest billions of dollars to match its capacity. The singular reason that TSMC is not a product company also works for it as it does not pose a threat as Samsung does when it makes product parts for Apple.

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Keith Sabine
Keith Sabine
10/17/2014 8:11:39 AM
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Newbie
Re: Layout is vital
While traditionally people did route critical nets first, and sometimes finish the routing of non-critical nets automatically, the problem with this approach is that you need a good placement as a starting point. 'Good' means you can complete the routing without shorts or opens. Because placement didn't consider routing, or merely made some estimate of it, designers often ended up doing things manually, This can take hours - even for just an opamp.

Animate solves placement and routing as a single problem, so no experimenting with different placements until you get a routable result. And you can set constraints on critical nets such that e.g. the width, spacing, shielding etc. are honoured. The same opamp can be placed and routed in seconds, and you don't get just one result but many, so you can pick the one you like, and get parasitics for simulation much earlier than by any manual method. You can then tweak the layout either by altering the constraints or by manual editing.

Of course some types of layout will probably never be automated, like RF for example. But for many applications such as IP generation where time is critical, automated layout offers real benefits over traditional manual layout.

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analoging
analoging
10/12/2014 8:49:56 PM
User Rank
Blogger
Re: Layout is vital
More companies have become chip design firms over fab based providers to reduce capital costs. TSMC has become the leading chip provider in the world as more companies outsource production overseas. It also makes TSMC's job easier as it can consolidate designs for a larger common customber base but it stunts creativity and innovation in the industry.

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fasmicro
fasmicro
10/11/2014 3:21:56 PM
User Rank
Master
LVS is important for accuracy
 However, accurate simulation of the design requires early layout and, with it, parasitic extraction, to be able to model the LDE effects during simulation.

Always do good LVS with accurate models of the parasitics. This is the most important aspect of this business. If your models are not good, you have no chance of success. Layout Vs Schematic (LVS) will help fix any issue that can make the layout not to match the schematic. Your CAD must have a good one for you to have a great product

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goafrit2
goafrit2
10/11/2014 11:02:32 AM
User Rank
Master
Layout is vital
>> An automated analog layout tool, such as Pulsic's Animate, can identify constraints intended by the designer and rapidly generate multiple real layouts in minutes. 

Analog layout is a big element in analog design. While a mixture of autorouting and manual works, I think the best model remains to manually rout all the critical signals. Layout is a big design phase that must be invested. Auto-routing works but not for all signals.

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More Blogs from Keith Sabine
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