Hello David.
On 08/20/2018 06:19 AM, David Lanzendörfer wrote:
Hi Hagen We could theoretically just use a Pierce oscillator, because you've already drawn the inverter circuit and could test this way, which one performs best to generate a square clock signal? What do you think? An idea for a test structure? https://en.wikipedia.org/wiki/Pierce_oscillator
Well, I am not sure, what you want test with that oscillator. Usually, this kind of quartz crystals are used since the eighties for microcontroller, often with both input pins. The frequency is determined by the crystal while the inverter is used to "shape" (having a significant magnification, the sinus waveform gets over-amplified - coined "endless") into a square waveform with cut-off areas (limited by the power supply).
We can not measure many helpful stuff out of this oscillator for our test waver. Or I do not see the point.
On Pearlriver we already have a space problem. The test pads consumes a lot of area for itself and for the distance between each other. We should concentrate on the values we like to get - what are resistance and capacitance for Poly, N+, P+, Metal etc and transistor parameters. If all layer processed fine it would be our bonus to see the ring oscillators running and measure the delay times over the minimal-sized gates.
Regards, Hagen.
P.S.: Usually the inverter is a Schmitt trigger (https://en.wikipedia.org/wiki/Schmitt_trigger) which has internally an extraordinary circuitry. Designing the StdCellLib further, a Schmitt trigger is on the list for input pads. Than I like to measure the hysteresis - which I can't with an oscillator.