Ultra Precision Reference LTZ1000

[GigaJoe]

im not sure about TL082 - it magnitude worse ...
old one AD708 , OP177F - single ; or a bit modern:  ADA4077-2B

personally i would go to chopper like OPA2188  , or more expensive type ..

[Andreas]

thats only what I have on hand right now... this board will get a TL082 as soon as I'm back home.

The TL082 needs a negative supply in this cirquit (common mode input range will be violated with input 0.7V above negative rail)
And I fear that the open loop gain is much too low for a good regulation.

with best regards

Andreas

[grx]

You're right. Oh well, this is for a test and the lt1013 has little chance of being destroyed so it may stay.

This is just a temporary card guys, just so I can test how everything works before I bring it the real expensive stuff.

[MiDi]

Nothing wrong with LT1013 around LTZ/ADR1000, it is proven design and the drift has plenty rejection, see e.g. https://www.analog.com/media/en/technical-documentation/data-sheets/adr1000.pdf#page=8.
I recommend to keep LT1013, for output buffer recommendation is ADA4522 or OPA189 - you do not want to use the zener output directly (only if you know what you are doing).

[GigaJoe]

And I fear that the open loop gain is much too low for a good regulation.

for TI OP07 it defined as 100 to 400 V/mV , so worse case 1uV change to output 100mV , IF it open loop ...
aside of very specific case i'm not sure if open loop of non outdated opamps are relevant for most schematic  .. 
TL082 (081) defined as 120dB or 120 dB → gain = 10^(120/20) = 10⁶ V/V = 1000 V/mV

[GigaJoe]

Nothing wrong with LT1013

True ..  let's introduce "Guaranteed Low Drift: 2μV/°C Max ; Guaranteed Offset Voltage: 150μV Max "  and then we will fight around it ...  are we live still in 80's

[grx]

There is no question that the LT1013 is the most widely used and probably the best opamp for the LTZ1000 and I am not bringing that point again.

The LTC2057 can also be used, but you need two. I made a carrier board to replace a LT1013 by a pair of LTC2057 btw :-)

I got temperature regulation by raising the set resistor a bit, to 13.5k (27k//27k)

It is very fun to see the collector voltage going down until it reaches the setpoint and then stays here
And then it goes haywire when I blow on it and then it slowly stabilizes again

Of course everything is very unstable since this is a faked discrete LTZ1000, but it works!
Again the goal of this board is not to be a reference but a testbed to understand and explore the behaviour of the circuit.

[GigaJoe]

There is no question that the LT1013 is the most widely used and probably the best opamp for the LTZ1000 and I am not bringing that point again.

Serious doubt .. when LTZ introduced in 1984 there is little alternatives was , 4Mhz chopping amplifier like alien technology ...

[grx]

TBH I dont understand the point of your last remarks, in the context of this topic.

[floobydust]

Long ago there was a fight between two experts here on using CAZ op-amp or not. It did not end well. There was blood.
The LTC2057 input as a pulsating switched-capacitor load, with the one view that is not good for the ref IC, something about knocking valence electrons out being bad for the lattice aging.
The repetitive capacitor charging seems to be the concern. Out of my expertise. I'd have to look for the posts.
Second view was the superior technical specs of CAZ for offset and drift, despite the HF carrier presence, are better than an LT1013.

Found the 2018 post:

Dr. Frank -

I can tell you what I can, because that's the same info LT / ADI will tell you when you work with their apps engineers.  Otherwise all our customer test data is owned by our customers.

So I guess that makes me full of crap - but it is expected.  I totally get it.  As I pointed out - I'd run my own tests and verification too.  That's a good way to do it.

What we see for drift rates:
In general, drift rates on the LTZ's we've built are fine, rarely no more than 4~5ppm/yr, usually less.   After 20 ~ 30 years too.  Some outliers down in the 1ppm/yr and over 6ppm yr, probably at least 20% are 2~3ppm.  Depends on each individual and application.  Basic datasheet circuit - sometimes with resistor mods as requested.   We don't run the LTZ's particularly cool, but not hotter than they need to be.  A lot depends on the thermal conditions  they see in actual use too.  Typical heater ratios are 13.25k to 15k over 1k.  Maybe even 16k over 1k if that is called for.  Depends on what cooling / heat sinking is available or not.

We don't ever bother adding the 400k resistor to adjust TC.  If you dial that in to an ideal setting today that might not be the ideal setting for later on - and that's only useful for a narrow temp range anyway.  What's more important (for us) is a stable and predictable TC - then you can add a temperature compensation factor into the system downstream (Which RHB should really like!!).

Never have we had to add extra caps to meet noise spec. - but then again we don''t run naked boards at customer site either - that's not the best idea for precision circuits.  If adding caps is the only way they work for you then that's how your setup works.  I won't argue with success  That being said I'm looking at an LTZ right now that's sitting in its open box, 13.25k over 1k, LTZ covered,  running on a linear power supply at 15V, PWW's and it's noise is <<1.2uV p-p.  Which is spec.  Just the datasheet circuit, nothing at all fancy, no slots or cutouts, no expensive resistors, etc.   

Zhtoor - Yes, it's all about heat flow.  Be careful about probing the circuit while it's in operation, because that probe in itself changes the thermal characteristic.  All pins really want to be same temp, but not all pins have the same thermal resistance to the die!

IN GENERAL - A chopper amp with a lower Ron on the input switches and higher charge injection combined with faster switch time can be more influential on the lattice aging.  I'm talking about chopper amp's effect on lattice aging, not outright destruction of the LTZ (although edge cracks are a possible failure mode of the LTZ die - but you usually see that on extreme thermal cycles or short circuits,  etc.).

Chopper amps USUALLY don't have the input current spikes spec'd AT CHOPPER FREQ.  BUT one suggestion is when you measure an amp for yourself you can then build an LTSpice model to play around with how the front end works.  The chopper amp simulation in LTSpice DOESN'T include the input current noise spikes in the chopper model...but there is another way.

Here is a CONCEPT ONLY example that models the switch currents of a 2378-20 SAR ADC; this is interesting since the front end switches are a cousin to some of the newer AZ choppers built by LT/ADI...This example is for an ADC not a chopper amp I know - it is showing what happens when the input switches are switching against the differential input caps.  But you can use a very similar technique to model the input of an AZ chopper amp.  You'll dial down and re-arrange the caps to simulate FET charge infection injection, but the process shown here should give you an idea how to build the chopper amp front end model in LTSPice to show you charge injection spikes, and maybe show how even a small RC filter will help:

http://www.analog.com/en/technical-articles/ltspice-simulating-sar-adc-analog-inputs.html

There is a video link at the end of the article -  especially interesting is the 50mA current spikes shown around 7 minutes into the video.  Which should pique your interest since you started out with just a 40pF cap on the chip and 1nF on your filter.  Low Ron of the switcher FETs and faster rise/ fall times will get you some serious current flows for sure!   

Again:  That's NOT the input to a chopper amp, I picked that as an online example as to how you might model chopper FET switching effects in LTSpice.  Be aware that some of the ADI choppers use a 4 phase or higher clock system - so you'll have to play around with the concept.

[GigaJoe]

LT1012 , LT1013 , was introduced 1987 . since 2015 -20 a lot of new stuff was introduced that outperform 35y old design . so why to drag it in ?
btw i remember about LTC choppers, and thing around (that in my view as assumption, as no really prove under microscope and reliable repeatable experiment that it a fact ) , again thing changes ...  not dragging to chopper , may other new alternatives 

[MiDi]

Than please provide evidence of significant improved performance with a modern part that replaces LT1013 in this application.
To be clear: we are talking about the oven and Iz steering and NOT the output buffer/gain stage for e.g. 10V.

[Kleinstein]

The LT1013 is not such a bad choice. With a single supply the OP-amps operate with some 0.6 V common mode voltage and this limits available precision OP-amps.
The LTZ1000 internal transistors provide additional gain (AFAIR ~ 200 fold) and the op-amp noise and drift are thus no fully effective. So 2 µV/K from the amplifier would contribute only one 0.01 µV/K for the reference output. Just from the data one might even get away with a LM358, but the LT1013 is clearly better.
There are not that many modern single supply precision OP-amps. With the ADR1000 AD sugested an ADA4084. However 0.6 V ist just at the transition where the NPN input stage starts to contribute - so more a poor choice that may or may not work.
Another possible modern choice is the OPA2145 - AFAIK it is used in a Hoki DVM. It's a JFET type, but on paper is low drift.

The main issue that I see with the LT1013 is the non standard pin-out for the SO8 case.

[laichh]

The reference board on my Hioki DM7275 has an op-amp with body marking of "TI45 2140", could be OPAx145, or OPA2140.

According to OPAx140 datasheet, Addendum Page 1, should be OPA2140 instead.

[exe]

Let me present you a cursed thing: the ltz999

I absolutely love this. In the past I wanted to build a poor man's oven-stabilized reference from a quad transistor array. One would be used as zener, one as a heater, one as a temperature sensor and one you can use anti-parallel.

[grx]

hehe. That was mainly for fun, as a complement to my "worse ltz1000 reference ever" (just the V1 of my own design) with standard components.

No one tried to build that thing before, because there is no real need for it I know Andreas has been using a discrete diode and transistor for testing, but that was a dead bug assembly.


Of all opamps, the LT1013 is the only one with THIS specification (see attachement), I never found a comparable spec anywhere else.

For a voltage reference circuit that pretends to rival with the best ones in the world, this seems quite an important one.

This op amp is still available everywhere for a reason, there is even a second source at Texas Instruments.

The OPA2140 does not report this info.

After more than 100 pages of topic it is quite unexpected that this choice of opamp is brought again on the table. No one in the topic ever suggested a better non chopper op amp. But okay, maybe it's the time to evaluate this, although I see little interest in this myself.

The LTC2057 has been proposed as an alternative, but it's a chopper one and there are potential issues with chopper noise. Also the long term drift has not been characterized. It's autozero right, but is this correction still working after several years? There might be secondary drift mechanisms that we are not aware of. I have no idea how to test that.

[iMo]

I'd avoid a chopper op-amp with an LTZ. Those switching pulses might hammer its silicon lattice so hard the dopants start packing their bags and leaving.
 

[Andreas]

It's autozero right, but is this correction still working after several years?

Read the datasheet more carefully:
"The LTC2057’s self-calibrating
circuitry results in low offset voltage drift with temperature,
0.015μV/°C (max), and zero-drift over time."

The main issue that I see with the LT1013 is the non standard pin-out for the SO8 case.

Who uses plastic packages (except choppers) for precision cirquits?
Look at AN-86: JW used the metal can package. See also:
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg448574/#msg448574
Nowadays I would use the CERDIP8 package of LT1013A from TI.

I'd avoid a chopper op-amp with an LTZ. Those switching pulses might hammer its silicon lattice so hard the dopants start packing their bags and leaving.
 

Don´t repeat this bad joke in times of KI. Some young beginners could believe it.

with best regards

Andreas

[exe]

Don´t repeat this bad joke in times of KI. Some young beginners could believe it.

Is there any evidence that this is a bad joke?

[tatel]

Nowadays I would use the CERDIP8 package of LT1013A from TI.

Where does one get that? All usual suspects seem to have just the plastic package available...

[grx]

ebay without a doubt, but I fear the customs now in europe. not good at all for all our hobbies (note: there is a topic for that, no need to develop the idea here)
I have a friend that gathers old electronics, but these are digital boards and the LT1013 is never found on these, even in old video circuits.

Of course metal can and cerdips are the best, but I wont stall my own projects just for this.
For starters I will study my PDIP references for a while. I am building three, and I have PTF56 resistors for two. I'll get more components in september I guess.
And then I will observe their behaviour. The only tool I have for this is a hp434401 with a seasoned reference. Not ideal I know, but I have no access to better tools.
Current step for now is building the real boards, I'm almost here, and I'm a bit afraid to solder an expensive ltz1000 and power it. I'll take maximum precautions.

[tatel]

ebay without a doubt

Unfortunately not, or at least, I'm only able to find DIP packaged ones on ebay right now

[grx]

yep it's not an easy find. I'll need to setup an ebay alert.

[tatel]

It could be purchased in quantity 50 directly from TI?

However I have absolutely no experience about purchasing directly from them. Should they ship via the usual pirates, wouldn't be willing to have anything to do with it. While I think cerdip packaging for LT1013 would be the more sensible option, it doesn't look viable to me

https://www.ti.com/product/LT1013AM#order-quality

[Andreas]

Nowadays I would use the CERDIP8 package of LT1013A from TI.

Where does one get that? All usual suspects seem to have just the plastic package available...

Hello,

recently I got it from RS-Components. (Order number 732-0847)
https://de.rs-online.com/web/p/operationsverstarker/7320847

But obviously it is no longer there.
I fear I will have to change to ADA4522 in future.

with best regards

Andreas