I have a board which fixes some issues that interfered with testing.
Since the opportunity was there, the input section has also been updated/improved based on comments and suggestions.
Perhaps more important, there is now support to run automated self-diagnostic/unit tests, which are nice and quick to iterate through, and that don't require ad-hoc code deployment or instrument setup.
Being able to route precision voltages around the board using the board calibrator/ dcv-source, works really well.
And getting the test setup vector/ as well as expected-behavior managed programmatically, and locked down in code, is progress of a kind.
It is an interesting property that the input conditioning may be able to measure it's own leakage, and switching charge contribution,
And with different input dc biases.
With the tests in place, the analog switches can be progressively added, and change observed.
test method,
test05 charge cap to +10V. hold 10sec for cap DA to settle, then turn off/float primary himux switch inputs, and observe voltage. measurement is taken from boot buffer/opa140 output.
test06 same except use -10V dc-bias.
test07 same except 0V dc-bias .
test08 charge cap to 0V/agnd, let cap DA settle. Put a +10V test on primary himux input (pin 5), while it is turned off.
test09 same except use -10V on pin5.
- with two hi muxes (U413, U402) fitted.
test05 -0.5mV/10s. = -0.5pA.
test06 leave 5mins for DA to settle. +1.7pA. 10mins. the same.
test07 5 mins for DA. 250uV/10s. +0.25pA.
test08 300uV/ 10s = +0.3pA.
test09 300uV/ 10s = +0.3pA.
conclusion - with just the adg1208 muxes, leakage is very controlled.
- add TI sn74lv4053 (U412) precharge switch, muxing boot. AZ switch (U414) is *not* fitted.
test05 +22pA. +21pA, 20pA.
test06 +23pA. +25pA. 25oA,
test07 +17pA. +20pA.
conclusion, a bit higher than might be hoped for,
- same test, as previous test except 4053 muxing signal.
test05 +20pA.
test06 +25pA.
test07 +22pA.
conclusion - 4053 switch position doesn't matter.
the 47p caps (C421, C428) are mlcc, and therefore a bit suspicious, but the voltage difference across them is very low.
board are well cleaned.
the copper guarding looks good to me.
the sn74lv4053 is salvaged from other boards, but that's because it had been demonstrated to work well.
I will try to add the previously shown AZ test modulation into the test suite- but am not sure charge-injection at ordinary AZ freq, will be evident above the leakage. I should probably re-review the previous 4053 tests, already posted to this thread.