Now that we have ADR1399/LTZ1000/ADR1000 I wonder if someone has finished one of the designs already?
Back in early 2021 I made simple voltage source with LTZ1000A and AD5791B as the main components.
Design requirementsIntended as voltage source for linearity sweeps, with short term stability and low noise as key requirements. INL was expected to be good enough for 5-digit-ish precision, but anticipated use was with external voltmeter.
Apart from +-15V DC voltage, AC range with maximal 10VAC and 50/60/100/400 and 1000Hz frequencies is provided, too.
How it worksThis is achieved in a single voltage range, +-16V, so it has some margin over desired range.
Base of this unit is AD5791B in datasheet configuration. DAC has voltage reference +-7V, taken from LTZ1000 source and opamp inverter to obtain negative reference. Output range +-7V is amplified by amplifier with gain of 2,3 to obtain desired +-16V range. Output capability of this amplifier is increased by LT1010 buffer.
It's driven by underutilized dsPIC33 microcontroller, display is bubble starburst, DL1414 type. RS232 for remote control is brought to the back panel.
PSU is unsurprising, toroid transformer with separate windings for earth-referenced logic and +-15V for floating analog section.
Each section (analog, PSU, digital) has separate compartment in the enclosure, with reference and DAC having its own plastic shield.
AC is done with simple sinewave lookup table (no DDS), digital interface is plentiful fast for this task.
ResultsI ran a quick DC INL check and found no surprises over what I expected, see attachment.
Despite being designed as test source for short term stability, I found it was quite stable. It drifted approximately -4ppm after being continuously powered for three months (most of the drift happened in first week, likely relieving stress from soldering) and stayed there since then (~18 months) within 1ppm range. I can only compare it against a single Solartron 7081 and bunch of 6 digit meters with LM399 reference, so not much of a metrological value in those.
Things to take a look atI made this as a tool for my personal use, from what I had lying around. No design files attached here, as this project is somehow untidy and half-baked, it takes a bit of effort to make it publishable. On the other hand - I really doubt anyone would replicate it and no particularly big surprises are hidden in this design to learn from.
I collected a bunch of higher-resolution photographs in an imgur album here
https://imgur.com/a/W15Z97J and shaky video of output switching by 1V steps
ResumeAD5791B works as datasheet says. LTZ1000A too.