# Triangle vs. Ground: What's the difference?

Discussion in 'General Electronics Chat' started by Rogare, Mar 20, 2012.

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1. ### Rogare Thread Starter Member

Mar 9, 2012
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Hello,

In the AD633AN datasheet, there is a diagram for "Squaring and Frequency Doubling" (p. 8). In the diagram there are ground symbols used at pins 5 and 8, but triangles used at pins 2, 4, and 6. What's the difference?

Thanks!

Dec 31, 2010
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3. ### MrChips Moderator

Oct 2, 2009
18,679
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Look at post #5 on this thread:

You will see three symbols for ground, Signal Ground (Common), Earth Ground and Chassis.

Earth Ground is used for electrical safety.
Chassis is the metal box of your equipment. This is wired to Earth Ground through the GREEN wire (in North America) on the 3-wire AC cord.
Signal Ground or Common is the 0V reference point in your circuit. If there is no connection to Chassis Ground, then your circuit is "floating".

It is common practice to connect Signal Ground to Chassis Ground.

There should be no current flowing from Signal Ground to Chassis Ground to Earth Ground.

4. ### Rogare Thread Starter Member

Mar 9, 2012
78
0
OK, thanks for the replies—much appreciated.

I built the circuit, but it didn't turn out as expected: for a 3V input, I was expecting a 0.9V output, but got about half of that. For a 0.5 input, I was expecting a 25 mV output, but the DC offset alone was 40 mV. (The output should be Vin^2/10.)

So, I think I may not have understood the grounding correctly. The circuit I built is diagrammed in "My Circuit.jpg" and the reference from the AD633 datasheet is in "AD633 Reference.png." Does anything seem glaringly off?

(Minimum operating range for the chip's supply voltage is +/- 8 V.)

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5. ### BillB3857 AAC Fanatic!

Feb 28, 2009
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I would insure that both batteries are supplying exactly the same voltage. If the supply is unbalanced, output will loose accuracy.

6. ### Rogare Thread Starter Member

Mar 9, 2012
78
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OK, I'll do that. Does the grounding look OK? I'm still a bit unsure about which type (triangle vs. parallel lines) are used where.

7. ### ErnieM AAC Fanatic!

Apr 24, 2011
7,980
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I believe the different ground symbols are intended to keep noisy things away from quiet things. Typically such a scheme is used for a "digital" (noisy) and "analog (quiet) ground.

Try connection all the grounds together at one point, meaning one wire between them on the board you have. The grounds still need to connect, just at one point to prevent circulating currents bouncing off ground.

("circulating currents bouncing off ground" is not quite a technical description but I pray it gets the point across.)

8. ### Rogare Thread Starter Member

Mar 9, 2012
78
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OK, yes, that makes sense. Thanks!

Nov 9, 2007
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10. ### leonalee New Member

May 17, 2015
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Maybe too late but it useful to the users, check out below source, good source to find of which symbol and what about it is.

<snip>

Last edited by a moderator: Jun 28, 2015

Jul 18, 2013
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And a pet peeve of mind as a few previous posts will attests to.
I have always taken issue with the likes of the 'Art of Electronics' as using the earth ground symbol throughout the book.
Where IMO it should be either chassis or logic common, unless they specifically wanted to indicate the common is earthed.
http://sites.ieee.org/ctx-emcs/files/2010/09/Archambeault-Ground-Myth.pdf
Max.

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12. ### Wendy Moderator

Mar 24, 2008
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Tsk Tsk, necroposting and hijacking at its worst. Both are not really allowed here.