xDevs.com 发表于 2024-3-10 11:08:32

Multi-chip LTZ1000/ADR1000 xDevs.com QVR reference

本帖最后由 xDevs.com 于 2024-3-10 11:18 编辑

Some years back in 2019 I wanted to experiment with lowering noise on DC zener reference. Best commercial reference - LTZ1000A has ~1uV noise peak to peak 0.1 - 10 Hz. This is only ok for 7 digit, but not 8 digit.
Because we don't have lower noise and better stability DC reference without quantum standard - we don't have 9.5-digit DMM in 2024. But what is one combine multiple LTZ1000 together into averaged output? If we take 4 chip noise should reduce by SQRT(4) = 2x times.
So we should see 0.5 noise pk-pk. If we increase zener current from 5mA to 10mA we can further reduce noise. So I designed quad-zener reference board and here are some results and photos.

Later I also build same reference device but with new ADR1000 chips (500 nV noise pk-pk 5mA).

https://xdevs.com/doc/xDevs.com/QVR/block_blk.png

Each zener core cell is individual output, opamp, resistors, heaters. Only the power regulator input is same (LT3045 low noise +12V). This let me to use reference as 4 separate 7.1/6.6V outputs or combine with passive resistor network to averaged low-noise.

https://xdevs.com/doc/xDevs.com/QVR/qvre_pcb_rev9.png

PCB is 6-layer RO4350 to reduce effects from humidity on SMT opamps (TI OPA2140) and SMT resistors/capacitors.

https://xdevs.com/doc/xDevs.com/QVR/test_qvr2_mk2/qvr_stackup.jpg

Assembly of all SMT parts done with reflow owen. LTZ chip and VHP resistor mount by hand with low temperature to avoid thermal stress.

https://xdevs.com/doc/xDevs.com/QVR/img/qvr2_top.jpg

One of ideas to try this low-noise reference module was to upgrade HP 3458A :

https://xdevs.com/doc/xDevs.com/QVR/img/qvr_swap_1.jpg

And measured noise with 4 x LTZ1000A chip, 10 mA current, using 80dB enjoydiy amplifier 0.1 - 10 Hz:

https://xdevs.com/doc/xDevs.com/QVR/test_noise_qvr2b/xDevs_noise003.png

250 nV peak to peak @ 7.1V , pretty good :). xDevs.com QVR consume about 160mA @ +13V and 5mA @ -13V for power.

I also tested many more ADR1000 and LTZ1000 chips (125 pcs total). ADR1000 noise is very good, usually about 450-500 nV pk-pk.


https://xdevs.com/doc/xDevs.com/QVRA/lf_noise_chart.png

Later in 2022 and 2024 I've built some more modules with ADR1000 to test long-term drift and noise too.
Three QVR module (4 ADR, 2 ADR and 1 ADR) are tested for long-term drift with nV-meter and DataProof 160A scanner. Drift compared to calibrated and stable Fluke 732A and LTZ1000A xDevs.com FX units.

https://xdevs.com/doc/xDevs.com/QVRA/ltd_chart_10khrs_blk.png

ADR1000 show drift about -2 ppm/year when running at lower +50 °C oven. No special aging or preconditioning was done before assembly.

https://xdevs.com/doc/xDevs.com/QVRL/img/ltdqvr_3da_1.jpg https://xdevs.com/doc/xDevs.com/QVRL/img/ltdqvr_3db_1.jpg

Later I built separate module with mixed LTZ1000ACH, LTZ1000CH and two ADR1000 different datecode.

https://xdevs.com/doc/xDevs.com/QVRL/img/ltdqvr_ltzqvr.jpg

Tested and adjusted for good temperature coefficient using "400kOhm" feedback resistor fine-tune:

https://xdevs.com/doc/xDevs.com/QVRL/cal/ltd_qvr0005_cell_abcd_tempco.png

And final block diagram..

https://xdevs.com/doc/xDevs.com/QVRL/img/block_ltd.png

Hope for good results in 2025...

https://xdevs.com/doc/xDevs.com/QVRA/qadr_posts_1.jpg

Low thermal TBP3 posts were used for best 5-way connection interface to the QVR reference module.

https://xdevs.com/doc/xDevs.com/QVRA/qadr_box_1.jpg

GitHub with results and more details : https://github.com/tin-/adr1000/

thy888 发表于 2024-3-11 17:12:34

外观设计很有FLUKE风格{:140_299:}

3458A 发表于 2024-3-19 16:47:24

基准和导图非常漂亮，祝你成功！！

bj549 发表于 2024-3-20 08:54:16

看起来很是牛b的样子。。。。
   
   祝贺楼主成功。。。

kevinstar888 发表于 2024-3-22 17:52:19

祝贺楼主成功。。。
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