IMHO the best way is to have
for 1 um
- 5 Volt VDD pads
- IO-Cells which working with 5 Volt
- and of course such Standard Cells
=> this give us all the stuff for Maker, Tinker, Geeks which dealing
with 5 Volt Circuits
for 0.8 um
- 3.3 Volt VDD pads, as well as 5 Volt VDD pads
- two Standard Cell Libraries, one for 5 V core Voltage, another for 3.3
core Voltage
=> this is a little bit hybrid, someone can use the technology for 5
Volt or for 3.3 Volt supply
for 0.5 um
- 3.3 Volt VDD pads
- IO-Cells which working with 3.3 Volt only
- Standard Cells for 3.3 Volt only
=> most circuits now can deal with 3.3 Volt also
below 0.5 um
- different VDD Supply pads
- different IO-Pad Cells for different power supplies
- Standard Cells at lowest Voltage which is acceptable
- Level Shifter between core area and Pad Cells
=> this becomes a mess
Here we should, at the least, think about differential IO-Pads, with
100..150mV swing.
The Voltage steps I am aware of are
- 5 Volt
- 3.3 Volt
- 2.5 Volt
- 1.8 Volt
- 1.5 Volt
- 1.25 Volt
- 1 Volt
The smallest feasible core Voltage seems to be 0.95 Volt. Otherwise the
trade-off between reducing the threshold voltages, the number of stacked
transistors which is still possible and the noise margin between low and
high levels will bite us in the ass.
On 03/13/2018 11:45 AM, ludwig jaffe wrote:
> One can have "5V-tolerable" 3,6V IO-Cells as TTLs High is only 3,6 V iirc.
> Having external current limit resistors at the pins exposed to 5v and
> internal diodes at
> the io pins against gnd and vcc to carry away the current this could work.
> xilinx does so with some fpgas with application notes that one can use
> them for
> 5v io.
> But be warned, if there is current creeping in from the IO-Ring to the
> VDD of the chip,
> the IO-Voltage ring needs to be limited in voltage as the current
> rushing in can lift up the
> 3,3V rail, so one needs an external transzorb diode to eat up the
> exxesive voltage.
>
>
> On Tue, Mar 13, 2018 at 6:36 AM, Hagen SANKOWSKI <hsank@posteo.de
> Libre-silicon-devel@list.o2s.> <mailto:hsank@posteo.de>> wrote:
>
>
>
> On 03/13/2018 11:13 AM, David Lanzendörfer wrote:
> > Hi
> > So I'd say we for now indeed just do 1um and then just run a 500nm node on
> > 3.3V only for SoCs and thelike.
> >
> > After all, these SoCs and CPUs usually get a 3V3 rail from the ATX power
> > supply anyway.
> >
> > But yeah, if 5V tolerance is required in 500nm technology we will have to use
> > the l=1um transistors from the 1um technology within the l=500nm technology
> > for the buffer transistors.
> >
> > Maybe we make "modular pad cells" which can be modified to provide 3V3 instead
> > of 5V as well to the internal logic?
> > Or maybe we just will have to modify our pad cells for the 500nm technology
> > and require two power supplies, one for IO and one for internal circuitry?
> > Or maybe have only one VDD and then a lot of linear voltage regulators built
> > into the CMOS chips?
>
> I'll think about that.
>
> Unified IO-Cells should not be an issue as
> - transistor sizes in Pad-Cells only depends on current they have to
> drive outside and the ESD protection diodes;
> - there limitation in size is and will be the pad size with approx.
> 90..100um by 90..100um itself.
>
> This is decoupled from our feature size.
> So, we can design IO-Pad-Cells with unified size, which applicable on
> all our technology nodes. In the end, the layouter will choose the
> Voltage-Supply-Cell he/she/it needs out of 5Volt, 3.3Volt or even lower
> cells.
>
> Voltage regulators are quite ugly while taking a lot of area and
> spreading heat into the die. And, we do not have transformers on die.
>
>
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