High Voltage ASICs
While operating voltages have been declining with each new process technology node, there are still applications that require higher operating voltages. These can range from analog designs that need high voltage, and to mature products operating off of 10 volt supplies.
Most advanced processes offer a dual oxide that can allow operation at 3.3 or 5 volts. The 5 volt oxide is designed for I/O operation but can be used everywhere to create a 5 volt circuit. But it does not allow 10 volt operation.
Figuring how to produce 10 volt circuits requires an understanding of wafer processing.
Some technologies offer EEPROMs or Flash memories. These technologies use about 14 volts internally in order to program and erase the memories. They create special transistors through the use of a third oxide that will operate at these voltages. Tekmos recognized that we could use those transistors to create true 10 volt circuits.
A 10 Volt Circuit
One of our first applications was a mixed signal circuit that operated off of a +/- 5 volt supply. Internally, the chip behaves as if the supplies were 0, 5, and 10 volts.
The part had high current drive requirements. This was not a problem since having a 10 volt gate drive allowed us to generate strong currents through moderate sized output transistors. Indeed, the outputs were so strong that we were able to reduce the Vol and Voh specifications. This reduced the power dissipated in the chip, and allowed for the removal of a heat sink that was previously required.
The TTL inputs also posed an interesting problem. TTL input signal specifications are 0.8 and 2.0 volts, referenced to ground. This is typically met in 5 volt designs through the use of a ratioed inverter set to switch at 1.4 volts. But since the chip ground is the most negative voltage, the TTL input specs became 5.8 and 7.0 volts. This would be impossible to meet with a ratioed inverter. We solved this problem by creating an internal voltage reference of 6.4 volts and used that in conjunction with comparators to create a translated TTL switching level.
Can we go higher? Yes, but conditionally. The processes we use have high voltage transistor options, some with voltages in excess of 100 volts. These are designed for output transistors, but we could make a chip that will operate at any voltage up to that level.
There are limitations. The high voltage transistors are slow, and so the resulting chip will be slow. And with the slow rates at these voltages, combinational logic will tend to have glitches. This will require a good deal more design effort.
But it can be done. Contact us for more information as to how we can apply this technology to your application.