12 bit A/D converter.....

EDAboard.com Forum Index -> Professional Hardware and Electronics Design

Author

Message

Trishool

Joined: 12 Jul 2001
Posts: 81
Location: Himalayas.(mount K2)

27 Aug 2001 20:56

Hi Guys,
I have been using 8bit A/D converters but my present application requires 12bit so I have choosen this TLC 2543CN from Texas instruments. There is a small problem hope you guys could hlp I need to drive it with external XTAL instead of giving pulses from uc .Can anyone help me
with appropriate schematics .Any schematics proven one for 12bit AD converter welcome .

Thanks in advance
________________
[img]upload/2734/Lt.gif[/img]

[ This Message was edited by: trishool on 2001-08-28 08:45 ]

Trishool

Joined: 12 Jul 2001
Posts: 81
Location: Himalayas.(mount K2)

28 Aug 2001 8:48

Hi ,
Topic changed Smile

any help now guys .....
Thanks

Trishool

Joined: 12 Jul 2001
Posts: 81
Location: Himalayas.(mount K2)

24 Oct 2001 14:35

Still looking.....

aNdreiBuuu

Joined: 30 Apr 2001
Posts: 387
Helped: 11

24 Oct 2001 14:49

use AD7893
best,
//a

MITSUKO

Joined: 06 Jun 2001
Posts: 49

27 Oct 2001 22:40

You could also use LTC1286 .
12 Bit serial AD with integrated s&h circuit .

Mitsuko

sintis

Joined: 28 May 2001
Posts: 28
Helped: 1

29 Oct 2001 11:41

Quote:

On 2001-10-27 22:40, MITSUKO wrote:
You could also use LTC1286 .
12 Bit serial AD with integrated s&h circuit .

Mitsuko

Or cheap equivalents from Microchip MCP320x series

Alexg

Joined: 14 May 2001
Posts: 51

29 Oct 2001 12:22

Hi,

Be very carefull with the board layout when doing 12 bit conversions. It is pretty hard to get more than efectivy 10 bits if you do not make a good ground plane, isolate as much as possible the digital and analog side of the circuit and have very solid power connections right under the AD converter. There are some nice application notes on the subject that are well worth reading. Do a google search and you will fing many. Microchip has a nice and simple one.

Best regards,
Alexg

2000

Joined: 14 May 2001
Posts: 89

29 Oct 2001 13:52

hello friend,

I've already used ads7812 from b*u*r*r*b*r*o*w*n* now T*I*... its a bipolar single supply serial 12 bits AD, and has also internal reference. They give samples of him really fast. It's precision is really a problem, because I'm using its internal reference that have a drift and its intrinsic precision is +-1LSB... so...
There is also ads7813 that is 16bit pin compatible with 7812...
Depending on what do you need this guy will work fine...
Suggestion: if you really need 12 bit precision try to use a 16 bit AD and take care on your layout...

good luck...

2000

2000

Joined: 14 May 2001
Posts: 89

29 Oct 2001 13:54

sorry,

no way to use external xtal....

2000

Alexg

Joined: 14 May 2001
Posts: 51

29 Oct 2001 17:40

Using a 16 bit a/d only will not solve the reference problem, the digital noise problems or the power supply rejection problem ! You have to really take very good care on those items if you want more than 10 bits real precision. It is quite and engineering task to get full 12 bits precision unless you do not have any size limits and can work with a 4 layer board.

Best regards,
Alexg

Trishool

Joined: 12 Jul 2001
Posts: 81
Location: Himalayas.(mount K2)

29 Oct 2001 21:38

Quote:

On 2001-10-29 11:22, Alexg wrote:
Hi,

Be very carefull with the board layout when doing 12 bit conversions. It is pretty hard to get more than efectivy 10 bits if you do not make a good ground plane, isolate as much as possible the digital and analog side of the circuit and have very solid power connections right under the AD converter. There are some nice application notes on the subject that are well worth reading. Do a google search and you will fing many. Microchip has a nice and simple one.

Best regards,
Alexg

Hi Alexg,
I am reading data from the ADC TLC2543cn ,But least significant digits are hardly stable it is stable only up to 1 decimal place ,which is making me hasty as when ever I read my temperature sensor I could read a difference of 2 degree C .What would you suggest is this a problem with the reference voltage applied ???.i have made the demo board for the time being but will consider your suggestions isolations I have already done should the reference to ADC and its VCC be seperated from the microcontroller also??

Thanks
Ts

PS: My many Thanks to all of you guys for your helpfull suggestions.

_________________
Regards
LET PEACE AND PEACE AND PEACE BE EVERYWHERE
[img]upload/2734/Lt.gif[/img]

[ This Message was edited by: Trishool on 2001-10-29 20:42 ]

Alexg

Joined: 14 May 2001
Posts: 51

30 Oct 2001 0:59

Quote:

On 2001-10-29 20:38, Trishool wrote:
when ever I read my temperature sensor I could read a difference of 2 degree C .What would you suggest is this a problem with the reference voltage applied ???.i have made the demo board for the time being but will consider your suggestions isolations I have already done should the reference to ADC and its VCC be seperated from the microcontroller also??

Usually the greatest noise generator are clock circuits and the microcontroller itself. If you have a single microcontroller and the AD converter use 2 different 78L05 regulator for each one !! They are cheap and in that way you will pretty much isolate the VCC noise. Use a HUGE ground plane for your analog circuit and another one for the digital part of the circuit. Do not make just one big ground plane. Connect the analog and digital grounds right under the AD or at the power supply. I prefer under the AD, but many different opnions there. Is your sensor stable enough to give you better than 2 C measurements ?? How fast do you need to measure ? If you do some readings and take use a moving average filter you might get better results because random noise tends to be cancelled. Many things to look at !! Check on the ones above and tell us how it goes. Do a search at microchip, they have a nice app note on 12 bits AD board layout.

Best regards,
Alexg

Trishool

Joined: 12 Jul 2001
Posts: 81
Location: Himalayas.(mount K2)

30 Oct 2001 13:44

Quote:

On 2001-10-29 23:59, Alexg wrote:
Usually the greatest noise generator are clock circuits and the microcontroller itself. If you have a single microcontroller and the AD converter use 2 different 78L05 regulator for each one !! They are cheap and in that way you will pretty much isolate the VCC noise. Use a HUGE ground plane for your analog circuit and another one for the digital part of the circuit. Do not make just one big ground plane. Connect the analog and digital grounds right under the AD or at the power supply. I prefer under the AD, but many different opnions there. Is your sensor stable enough to give you better than 2 C measurements ?? How fast do you need to measure ? If you do some readings and take use a moving average filter you might get better results because random noise tends to be cancelled. Many things to look at !! Check on the ones above and tell us how it goes. Do a search at microchip, they have a nice app note on 12 bits AD board layout.
Best regards,
Alexg

Hi
It would be good if the link is given here I searched but couldnt find any.

Regds
Ts

johnyaya

Joined: 30 May 2001
Posts: 149
Helped: 17
Location: YoyoDyne

30 Oct 2001 18:14

Alexg - Not entirely true about single ground planes. Printed Circuit Design magazine ran an article about using ground planes with analog and digital circuits. Good reference article.

Alexg

Joined: 14 May 2001
Posts: 51

30 Oct 2001 20:09

Quote:

Hi
It would be good if the link is given here I searched but couldnt find any.

Regds
Ts

You did not look well enough Smile

Here it goes, it is a simple app note but quite informative app note AN688:

http://w*w.microchip.com/11110/suppdoc/appnote/category/analog/adc/6857/index.htm

Best regards,
Alexg

Alexg

Joined: 14 May 2001
Posts: 51

30 Oct 2001 20:17

Quote:

On 2001-10-30 17:14, johnyaya wrote:
Alexg - Not entirely true about single ground planes. Printed Circuit Design magazine ran an article about using ground planes with analog and digital circuits. Good reference article.

Like many other things in electronics.. Your mileage may vary depending on your application. Usually you want to make a clear current path for each section of your circuit. Analog ground plane returns analog noise and digital ground plane returns digital noise. If you have the current path well done in power planes than I guess that you might be better off with just one big ground plane. If you are working just 2 sided boards and are returning ground current for all the circuits trough the ground plane you are better off using 2 ground planes and connecting them together at just one point. I usually try to make my sensitive boards work without any ground planes in the early prototype stages and just then put the ground planes to optimize things. This way I can clearly see if I made any big mistakes in the ground return paths.

Is the article you are talking about online ? I will search for it but if you have a link handy I would appreciate it.

I have made some boards with 140 db dynamic range and I would love to have more clear information about layout techniques. Everything seems to be a little like black magic. You get small pieces of advice here and there but no one has all the information condensed in just one place. For the digital guys "High speed digital design" is a great book.

Best regards,
Alexg

Best regards,
Alexg

Trishool

Joined: 12 Jul 2001
Posts: 81
Location: Himalayas.(mount K2)

31 Oct 2001 16:56

Alexg

Thanks The Article is really a worth reading and very Interesting.

_________________
Regards
LET PEACE AND PEACE AND PEACE BE EVERYWHERE
[img]upload/2734/Lt.gif[/img]

[ This Message was edited by: Trishool on 2001-10-31 16:03 ]

Alexg

Joined: 14 May 2001
Posts: 51

01 Nov 2001 5:36

Quote:

On 2001-10-31 15:56, Trishool wrote:
Alexg

Thanks The Article is really a worth reading and very Interesting.

It is a nice little compilation of most of the important stuff. If you need something more specific in that area I might be able to help. I had to gather lots of material for a project I made and I have everything printed in paper and archived in the deeps of some closet Smile

If you need more help I can dig some information for you.

Best regards,
Alexg

johnyaya

Joined: 30 May 2001
Posts: 149
Helped: 17
Location: YoyoDyne

01 Nov 2001 6:26

Unable to find the article in electronic form at the Printed Circuit Design (pcd) web site (pcdmag.com), so I scanned the 4 pages of the article (.jpg) and posted them at http://tryton.plocman.pl/gula-cgi/filemannew/fileman.cgi?wd=pcd
Well worth reading...

[ This Message was edited by: johnyaya on 2001-11-01 05:31 ]

Alexg

Joined: 14 May 2001
Posts: 51

01 Nov 2001 8:15

Thanks a LOT, Johnyaya

The article is absolutely great and clears up many topics that Mr. Ott does not even clear in his books !

It is indispensable for anyone doing mixed signals design. Very concise and complete.

Take a look at it Trishool it will clear up things even better than microchip's app note.

Best regards,
Alexg

EDAboard.com Forum Index -> Professional Hardware and Electronics Design

Page 1 of 1

All times are GMT + 2 Hours

Abuse
Administrator
Moderators

sitemap