Thermometer Code Chip

I'm looking for a chip that outputs a Thermometer Code.

I vaguely remember such a device. Is there one still made? ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Jim Thompson
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LM3914

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John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  
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John Larkin

Thank you! Google couldn't get me there :-( ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Jim Thompson

No, that's the dot/bar display driver, takes in analog voltage and displays on a set of LEDs.

If we're talking about a TO-92 packaged device that outputs a DC voltage depending on temperature, it was three numbers after the "LM" and close to the combination of numbers in "3914" but I cant' remember the exact number.

Michael

Reply to
Michael Black

TI's LMT70, LMT84 to LMT90?

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-TV
Reply to
Tauno Voipio

Those are temperature sensors, _not_ thermometer code.

See LM94022 on the Device Models & Subcircuits page of my website. ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
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Jim Thompson

Which decode pattern is often referred to as a "thermometer code."

Apparently, that's what Jim wanted.

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John Larkin         Highland Technology, Inc 
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John Larkin

Yes. ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
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Jim Thompson

More detail for the lurkers:

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John Larkin         Highland Technology, Inc 
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John Larkin

Not a firm 'yes', more of a 'maybe'; the input to that chip is analog voltage, and the outputs are regulated current sinks. It isn't a real logic-in/logic-out encoder, more of an A/D converter with display driver.

Reply to
whit3rd

It's a 10 bit unary ADC, and can be used as such. I've done it before. :)

Tim

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Tim Williams

Classic flash ADCs used 2^n comparators and a resistor string in the front end. The resulting (say, 256 bit) thermomometer code was then mapped into binary. I think somebody did that at 10 bits, 1024 comparators.

Nowadays people tend to do cleverer things.

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John Larkin         Highland Technology, Inc 
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John Larkin

They come in a wide variety of packages and range in cost from $0.50 to a couple of dollars in quantity. The number of outputs also varies widely, with both linear and analog ranges. What are you looking for specifically?

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Rick
Reply to
rickman

Opps, that should be linear and *log* ranges...

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Rick
Reply to
rickman

I sometimes use it to display the noise floor in laser-based instruments, along with some three-colour Avago LED bargraphs and a simple false alarm rate servo. (see

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).

Watching the lights flicker is a surprisingly sensitive test for subtle problems, such as the very beginnings of laser instability. You can see noise floor variations of a small fraction of a decibel, and correlate them with things like scan position.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
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Phil Hobbs

Are they still de rigeur for the bleedingest of edges in the Hittite and etc. catalogs?

Pipelined SAR has certainly come a long way since the olden days.

I've seen an oddly large number of DACs that claim to do this, even for 12 bits. Seems odd that they'd succeed in using that many resistors and MOS gates. Could well be that they're doing some R-2R action regardless, maybe even a bit of each (an R-2R chain is binary, but an R-R-..-2R-2R-.. network would work for any base; the classic resistor decade box being such a case, for N = 10).

Tim

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Tim Williams

Flash converters are the only choice for anything above around 1-2 MSPS last time I looked hard. Maybe they are pushing towards 10 MSPS with SARS and SD converters. But for anything higher a flash converter is the only choice.

That said, there are different forms of flash converters. Up to about

8-10 bits all that I have seen were single stage. But by the time you reach 10 bits the number of comparators becomes unwieldy. For high bit counts or for lower power they use subranging with a pair of lower bit count flash converters, one with low resolution for the upper bits and one with high resolution for the lower bits. Essentially this is a hybrid of the flash converter and an SAR. To deal with the imperfections in matching the two it is common to have an overlap in the number of bits used. These are are the bleeding edge devices providing flash like performance at up to 16 bit resolution.

But for the highest sample rates the direct flash converter is your huckleberry.

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Rick
Reply to
rickman

LM34 is a TO-92 analog o/p temp sensor. Nothing related to thermometer code though.

Reply to
Cloaca

When did you last look? Two decades ago? :)

All the ones I've seen (within say 5 years) from about 20 to 500 Msps and

8+ bits are pipelined SAR. Usually with terrible INL for the higher bits versions, but that reflects their usage: AC circuits, radio (SDR), ultrasound, etc., where low DNL is priority.

Often, they're also in a series, so you get like, 65-80-110 Msps and

10-12-14 bits. Likely they use the same configurable die for everything in that series, and burn some fuses during test to implement the highest spec the chip meets.

They either state what they are (pipelined SAR), or it's apparent from the timing -- usually LVDS, SDR or DDR output, where a given analog sample takes N+1 or so clocks to fully propagate through the chip. The INL/DNL graphs (if provided) also look much like typical SAR graphs; though I'll admit I haven't seen a wide breadth of ADC types to compare to.

A flash converter could get more data (perhaps more parallel LVDS lanes?), with less latency (maybe N/M + 1 cycles, where M is the ENOB of the flash stage), but those don't seem to be common, at least in the ranges I've looked at.

They often talk about "proprietary compensation stages" or something to that effect, suggesting that simply churning out a number in the conventional method isn't as simple when you're doing it at *that* rate. Maybe this is something they were missing, and hence why flash was the only option, back in the day?

They're also moving away even from 3.3V logic these days; the 1.8V parts are something like 1/4 to 1/8 the power for the same specs. And much, much faster at the top end.

Tim

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Tim Williams

Can you offer a few part numbers?

Not sure why you limit this to pipelined SAR. Subranging also has to do multiple steps which can be pipelined or not. But more importantly, there can be some "issues" at the edges of a range which require correction. In face, subranging flash converters are also referred to as pipelined... a rose by any other name...

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Rick
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rickman

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