How do We place Analog and Digital Blocks in a chip

[Prasanna Kumar]

Hi All,

I am doing full custom design. some times it requires that we have to have analog and digital blocks together in a chip. how do we take care of placing & Routing Analog blocks with Digital Blocks as well as I/O pads.

I have not understood the below mentioned 2 points for place and route.Can any one Please explain me ? I shall be great ful.

For a Place and Route tool What do we mean by "pitch" and how do we adjust it as per the P&R tool.

1. Minimun Number of access points:
UR ports should have minimum 2 access points either horizontally or vertically depending upon how METAL2 routing is allowed in ur process .    

2. ALL the ports should be on the minimum routing grid , as ur cell will be used by automatic place and route tool,which identifies only those ports which are given on Routing grid.

Thanks in Advance

 

[skymusic]

one pitch is equal the minimum width of vias plus minimum space between vias

 

[Teddy]

2) - tool will not route (and will gnore) those ports which are not on routing grid.

 

[layes2]

put analog at acorner
and guard it

 

[selvaraja]

Hi

protect analog block with guard band ... use dedicate pad for analog & digital block ..these to avoid any substrate coupling.

 

[yeechyan]

Use seperate vdd and ground pads for analog and digital blocks.

 

[manissri]

jusr go for the book " mixed signal design" by yanni.p.tsividis
manish

 

[rajath]

Analog and digital signals should not be running side by side. If this isolation is not possible due to space constraints, the lines can be seperated by putting a vss line between them.

 

[piao]

Besides above, Analog and digital need to use different VCC VSS bus supply, and sometimes you need to shield some signals.

 

[uncle_urfi]

For academic chips, it is a good idea to short the analog_VSS with digital_VSS using only the top-metal jumpers that can be severed later if desired. For PLLs, this results in better performance.

If you don't require this later, you can perform surgery. The other option (shorting the two grounds on chip after fabrication) is quite expensive.

Analog blocks should be surrounded by Guards Rings. The idea of a split-guard ring has been presented in literature and provides even better isolation.

Digital Lines running long distances esp. from the pads to a certain input, should pref. be running over an N-well so that the injection into the substrate is minimized.

+ many tips and tricks. Read the Art of Analog Layout by Alan Hastings.

 

[zx2051]

seperate them with thick guard ring

 

[parthi2311]

Hi selvaraja,

How to add guard band.? is there any material available? If so please share it. I ll be grateful to you.

 

[mikersia]

sonsivri.com might help