I have to admit, I'm in Edwin's camp here on LTZ vs caps discussion. 3458A's A9 don't use magic caps either, for what it's worth (yes, not great design for long stability otherwise).
More often than not spikes and other instability is caused by measurement gear or wiring or environment (EMI/RFI/power coupling) than reference itself. Trying to make reference more robust against external world influence is kinda going backwards.
Hello Illya,
you compare A9 board, which sits double shielded inside the 3458A, to 'our' standalone reference application, which all are definitely exposed to external EMI.
That comparison is not feasible, as it's definitely a different use case for the LTZ circuit.
Datron, as one of only two designers and suppliers of an LTZ based 10V reference (e.g. 4910) definitely has applied several components for hardening the circuit against external EMI. One feature are one or two 100nF parallel to the BE of the temperature sensing transistor, the other is an additional RC filter at the 1013 opamp for the reference amplifier.
I assume, that you still have that 7000 reference, maybe you can have a reverse engineering look inside that circuit, and I bet you will find similar circuit (as Mr. Pickering was working for Datron, as well as on the 7000, afaik).
Your argument, NOT to make the LTZ circuit more robust against EMI ('going backwards') is kind of strange, what do you propose, instead?
I can only contribute my own experimental experience, that these additional components really suppress external EMI pulses, but w/o any degradation of the long term drift.
All of my 7 LTZ circuits show an annual drift of less than 2ppm from start, and less than 1ppm after an initial run-in time of about half a year, despite all having these capacitors fitted.
The claims of Mr. Pettis, aka MisterDiodes, are not plausible to me, because he/they did never give any experimental proof for their claims, neither any detailed description, how/where their LTZ circuits were used, i.e. whether inside a hermetically shielded environment, or as a standalone application.
Also, any links to scientific papers about such supposed 'lattice degradation' are missing.
Therefore, I still consider Mr. Pettis objections to this case as being baseless, irrelevant and even misleading.
Frank