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how to make one parameter shared by bunch of stretch handles?

zssfred

In the official docs, cadence shows how to make stretchable handles for the metals on the source and drain of a MOS.

But it needs to define separate parameters for each metal of source and drain. It is simple but tedious. Especially, in multi-finger mode, it is impossible to define the required parameters because the metals on source and drain are variables.

There should be a data structure to tackle these issues. And it is already a common practice in lots of foundries' PDKs.

Anyone knows the detailed algorithm?

Thanks.

Fred

Parents

  • Hi Fred

    The simplest method is to use a DPL (Disembodied Property List) as the value of the stretch parameters to contain the stretch information. For a MOS device, I usually add parameters for the top drain handles, bottom drain handles, top source handles, bottom source handles and same for the gate ends if necessary.You could get by with one parameter but the value is a string which gets pretty long and takes some time to turn into a DPL and back.

    The parameter value is actually a string which is turned into a DPL with evalstring in the stretch handle function and the pcell function (I use the same code to parse the information for consistency).

    "(nil d1 .02 d7 .08 )" => (nil d1 .02 d7 .08)

    value->d7 == .08

    value->d3 == nil (not found) - No stretch, offset is 0.

    value->d3 = .04

    (nil d1 .02 d7 .08 d3 .04)

    The DPL value starts with a nil and has a key, value pair. The key is the stretch handle name, the value is the number which is subtracted from the "usual place" where the metal would be without stretching. I use subtraction because most of the time because the resulting string is shorter.

    The stretch handle function makes sure the value is within the constraints. It converts the DPL back into the string to update the parameter using sprintf:

    sprintf( nil "%L" DPL )

    The pcell subtracts the value from the usual place for the metal edge to calculate the offset and fills in the contacts accordingly. If a value is not found in the DPL, there is 0.0 offset.

    Ted

Reply

  • Hi Fred

    The simplest method is to use a DPL (Disembodied Property List) as the value of the stretch parameters to contain the stretch information. For a MOS device, I usually add parameters for the top drain handles, bottom drain handles, top source handles, bottom source handles and same for the gate ends if necessary.You could get by with one parameter but the value is a string which gets pretty long and takes some time to turn into a DPL and back.

    The parameter value is actually a string which is turned into a DPL with evalstring in the stretch handle function and the pcell function (I use the same code to parse the information for consistency).

    "(nil d1 .02 d7 .08 )" => (nil d1 .02 d7 .08)

    value->d7 == .08

    value->d3 == nil (not found) - No stretch, offset is 0.

    value->d3 = .04

    (nil d1 .02 d7 .08 d3 .04)

    The DPL value starts with a nil and has a key, value pair. The key is the stretch handle name, the value is the number which is subtracted from the "usual place" where the metal would be without stretching. I use subtraction because most of the time because the resulting string is shorter.

    The stretch handle function makes sure the value is within the constraints. It converts the DPL back into the string to update the parameter using sprintf:

    sprintf( nil "%L" DPL )

    The pcell subtracts the value from the usual place for the metal edge to calculate the offset and fills in the contacts accordingly. If a value is not found in the DPL, there is 0.0 offset.

    Ted

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