Precise & low noise voltage reference

Thread Starter

Edgar Gil

Joined May 10, 2018
5
Hello fellows,

I'm working on a project and I have the need to use analog to digital conversions, I need to get a precise and low noise voltage reference, in order to get more accurate measurements of course.

After reading a litte bit, I've found a couple of things that could be useful (I think)

My idea is to use a RC low pass filter like this:

To filter a 12V voltage input (switched power supply), with a 20ohm resistor and 2000uF capacitor, which gives a cutoff frequency of about 4Hz (according this calculator http://sim.okawa-denshi.jp/en/CRtool.php).

Once filtered, feed a circuit like this:


The LM4040DIZ-4.1/NOPB (5) is a voltage reference diode (according http://www.skillbank.co.uk/arduino/measure.htm) and feed with the Vref output an Op Amp as buffer to provide more current at that specific voltage. Of course R1 should be estimated again for this array (vcc 12V), to protect the diode.

My question is, am I right? or someone want to share with me another way to get a precise and low noise voltage reference.

Thanks in advance,
 

ericgibbs

Joined Jan 29, 2010
12,901
hi Edgar,
Welcome to AAC.
Add a 100nF cap across the 2000uF cap, it will improve the high frequency filtering.

E

BTW: what level of noise is acceptable.?
 

Thread Starter

Edgar Gil

Joined May 10, 2018
5
Hi Eric, thanks for your quick answer!

Do you mean a 100nF capacitor in parallel with the 2000uF?

I working on a prototype (personal project), so I have not a determinate specification, most of my work (in electronic) is achieved by trial and error due that I have not advanced lab measurement equipment, I have no way to measure the ripple voltage or waveform at the output.

Basicly I'm looking for community approval or recomendation of another solution based on your experience before start building something ;)

Thanks again
 

Thread Starter

Edgar Gil

Joined May 10, 2018
5
Thanks for your recomendations guys, also I've watched a video from Dave at EEVBlog explaining about the bypass capacitors.

Summarizing, I need to add another capacitor (ceramic or tantalum) for high frequency filtering, and this desing it's a good starting point for cheap and precise voltage reference, right?

Thanks again guys
 

ericgibbs

Joined Jan 29, 2010
12,901
As you and I do not know the load, it common sense to advise the TS to add an OPA buffer.

The TS clearly stated:
and feed with the Vref output an Op Amp as buffer to provide more current at that specific voltage



 

OBW0549

Joined Mar 2, 2015
3,566
I'm working on a project and I have the need to use analog to digital conversions, I need to get a precise and low noise voltage reference, in order to get more accurate measurements of course.
How precise? How low a voltage noise do you need? Measured over what frequency range? And what are your requirements regarding voltage shift with temperature?

All of these things matter, and it's important to express them in hard numbers; general terms like "precise" and "low noise" are meaningless since any given level of performance might be unnecessary overkill in one application, yet laughably inadequate in another.

The LM4040DIZ-4.1/NOPB (5) is a voltage reference diode (according http://www.skillbank.co.uk/arduino/measure.htm) and feed with the Vref output an Op Amp as buffer to provide more current at that specific voltage.
How much current? "More" isn't specific enough.

The LM4040 might be an excellent choice, or it might be completely inappropriate; we can't tell without specific performance requirements in your application.

It certainly wouldn't be my first choice for a voltage reference for most precision A/D applications; another reference, the ADR4540, would give you 5X better initial accuracy, barely a tenth of the voltage noise, and as little as 1/50 of the temperature shift.

But once again, the LM4040 might be perfectly OK for what you're doing, or it might not; it all depends on the actual level of voltage reference performance you require.

My question is, am I right?
Absolutely no way to tell, without numbers.
 

crutschow

Joined Mar 14, 2008
27,184
The TS clearly stated:
and feed with the Vref output an Op Amp as buffer to provide more current at that specific voltage
Yes, he certainly did and I missed that. :oops:
Initially he said he wanted an accurate reference to do A/D conversion so it's not apparent why he needs more current.

My thought on not adding an op amp is because that just adds a source of noise.
 

dendad

Joined Feb 20, 2016
3,835
Yes, real numbers for the stability and accuracy are needed.
For just a rough reference voltage, you can even get away with using an LED, so having a power indicator as well. But that is NOT a Precision Ref!
Numbers please.
Like, how many bits will your A-D use? That is a good starting point.
 
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