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@ -31,4 +31,10 @@ Once the unit was back home, ACAL ALL was run at various points during the drift
## U180 drift evaluation ## U180 drift evaluation
Now the big question with any 3458A project is whether the U180 ASIC at the heart of the meter is still in good condition. This requires an extensive check, powering the meter and monitoring the calibration constants from the ACAL DCV. I have written a toolkit for this (linked here). Although this is a rather short data capture, several captures were made. All with similar results in terms of the drift observed. Now the big question with any 3458A project is whether the U180 ASIC at the heart of the meter is still in good condition. This requires an extensive check, powering the meter and monitoring the calibration constants from the ACAL DCV. I have written a toolkit for this (linked here). Although this is a rather short data capture, several captures were made. All with similar results in terms of the drift observed.
![u180-drift](3458-WorkLog/U180-drift.png) ![u180-drift](3458-WorkLog/U180-drift.png)
## Improving
If one looks at semiconductor ageing there are a few things we can do to improve the stability in the long term.
Firstly, it is possible to lower the current passing trough the reference devices on the die, this in turn will decrease the drift experienced from electromigration. This is the movement of material caused by electons bumping into then. Thus this could be lessened by decreasing the amount of electrons troughout the device. This coming at the tradeoff of noise.
Secondly and majorly is chemical reactions over time, though stable a chip still exists upon a mixure of chemicals all slowly reacting on oneother. Thus [Arherrius' equation](https://en.wikipedia.org/wiki/Arrhenius_equation) comes into play, where reaction rates increase as temperature rises. Emperically this has been tested to double the drift for every 10degreesC.
Thus it is interesting lower the setpoint of the LTZ1000 voltage reference setpoint. Well known on the 3458A is the voltage reference being operated at an extremely high oven temperature. As such I have added a resistor to the voltage reference board at designator X413, decreasing the temperature to ___degC.