Speaker
Mr
Staf Verhaegen
(imec)
Description
One of the important steps when doing radiation hardening by design for mixed-signal and analog blocks is simulation of SET events. It is needed to find the SET sensitive nodes in a design and then adapt the design to bring the SET hardness in compliance with the specification. In order for an analog designer to do this efficiently the tools used should be integrated in the normal analog design flow. It should be flexible enough to screen for sensitive nodes in a design and later on focus on certain nodes. In analog design the timing of an event is important as a strike often only generates a non-compliant SET on the output when the circuit is in a certain state or transition. The timing may be dependent on the simulation corner and ideally the testbench should not need to be changed for this dependence. Additionally it should be avoided that a certain circuit has to be adapted to be able to inject an SET pulse in any node in its hierarchy.
Up to now for DARE development at imec a SET_STRIKER cell combined with a deepprobe cell was used. The SET_STRIKER is a model for the SET pulse generated by a single strike of a particle. The purpose of the deepprobe – included in the latest releases of analogLib included in Virtuoso IC – is to allow to inject in any node in the hierarchy of the circuit without the need of adaptions in the circuit. Alternatively, an ocean script is used to inject SET pulses in all nodes in a design. With the extensive use of these tools possible improvements were indentified:
* The single strike generated by one SET_STRIKER meant that for each event that one wanted to include in the simulation a separate instance had to be included in the testbench and the timing between the events had to be set manually. Each of the SET_STRIKERs had to be accompanied with its own deepprobe to inject in the right location. If one wants to do a simulation on only a subset of the nodes all the unwanted ones has to be disabled manually.
* The deepprobe only connected to one node so it was assumed that the injection always happened with the other end of the SET_STRIKER connected to either the ground or the supply of the circuit. This is most of the time the case as most of the time the bulk of a transistor is connected to one of these nets. When this is not the case two deepprobes should be used but that may be overlooked when setting up the test bench.
* The ocean script is mainly used for checking of standard cells and does not have the right capability to properly time the events as needed for analog radiation hardening by design and is not integrated in the analog design flow.
In the DARE65 project (contract no. 4000117214/16/NL/LF) then the SET simulation flow was improved based on the identified shortcomings:
* SET_STRIKER was extended with a SET_STRIKER_PERIOD and a SET_STRIKER_TRIG cell. These two cells allow to generate several SET pulses. The first cell generates events with a periodic repetition and the second one events triggered by an input signal.
* A dual deepprobe was made that connects to two nodes in the circuits. It uses a list of node pairs and can switch between the pairs during the simulation. Again two variants are available, one that switches periodically and one that switches triggered by external signal.
* A support window is available to get a list of all sensitive nodes in the circuit under test and select a subset of the nodes for simulation. This set can then be saved. It also allows to highlight the nets and nodes of the selected pairs.
* A second support window is available that allow to look up the nodes to which an SET pulse was injected in the circuit under test.
With these improvements implemented the analog designer now has a flexible tool set that allows to simulate all needed events with a single instance of a deepprobe and an SET pulse generator with the needed flexibility and efficiency to use it for SET hardness screening and problem fixing.
Summary
One of the important steps when doing radiation hardening by design for mixed-signal and analog blocks is simulation of SET events. In this paper the improvements to the SET event simulation flow for the DARE65 project is discussed that resulted in a flexible tool integrated in the Virtuoso analog design environment. It allows to screen SET sensitivity and simulate SET events efficiently.
Primary author
Mr
Staf Verhaegen
(imec)
Co-authors
Mr
Geert Thys
(imec)
Mr
Giancarlo Franciscatto
(imec)
Mr
Guillaume Pollissard
(imec)
Mr
Jan Wouters
(Imec)
Mr
Laurent Bertil
(imec)
Mr
Wim Sijbers
(imec)
