All About Circuits Forum How to explain? Resistors and Capacitors
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#1
03-31-2009, 11:16 AM
 Kyuman New Member Join Date: Mar 2009 Posts: 5
How to explain? Resistors and Capacitors

The tolerances in Resistors and Capaictors have a major impact on Analog circuits but not on Digital ones!

This is a statement that was made to me and I was asked to explain:

1. Is it true or not?

I have no idea how to approach this, can anyone help?
#2
03-31-2009, 12:20 PM
 Bill_Marsden Super Moderator Join Date: Mar 2008 Location: Dallas, TX (GMT-5 w/ DST) Posts: 19,042 Blog Entries: 5

Digital is usally all or nothing, so if a component is "close enough", it works.

Analog, on the other hand, is a bit like machining parts. Tolerances add up, if they add up the wrong way it doesn't fit.
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"Good enough is enemy of the best." An old engineering saying, Author unknown.

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#3
03-31-2009, 03:36 PM
 mik3 Senior Member Join Date: Feb 2008 Location: Cyprus, but now in UK (GMT+0) Posts: 4,846 Blog Entries: 9

In digital circuits, logic signals can be recognized as high or low bertween some voltage range. Thus, a small variation due to components tolerance is acceptable.

In analog circuits, tolerance of the components may affect the operation of the circuit at a high degree. Imagine that you design a band pass filter with a very high Q and the values of the components are not exactly as calculated due to tolerance. Because of the high Q of the filter a small variation in the components value can cause a significant variation on the bandwidth of the filter. This is an example of an analog circuit.
#4
03-31-2009, 08:17 PM
 kakin New Member Join Date: Mar 2009 Posts: 9

for analog it works something like
1.1 + 1.2 + 3.1 + 1.3 + 2.3 = 9

for digital
floor(1.1) + floor (1.2) + floor (3.1) + floor (1.3) + floor (2.3) =
1 + 1 + 3 + 1 + 2 = 8

9 ≠ 8

Now imagine if that were kiloVolts, 9kV is way bigger than 8kV...
#5
03-31-2009, 09:17 PM
 Kyuman New Member Join Date: Mar 2009 Posts: 5

So if I understand this properly.

Even if I use a 10% tolerance Capacitor instead of a 1% the quality of the signal will not be effected nor will the quality of the product?
#6
03-31-2009, 09:27 PM
 Bill_Marsden Super Moderator Join Date: Mar 2008 Location: Dallas, TX (GMT-5 w/ DST) Posts: 19,042 Blog Entries: 5

Depends, a lot of digital circuits have analog components. If this is the case it can matter.

In other words, only if we have the circuit schematic we can say for sure.
__________________
..
"Good enough is enemy of the best." An old engineering saying, Author unknown.

General info:
If you have a question, please start a thread/topic. I do not provide gratis assistance via PM nor E-mail, as that would violate the intent of this Board, which is sharing knowledge ... and deprives you of other knowledgeable input. Thanks for the verbage Wookie.
#7
03-31-2009, 11:59 PM
 thatoneguy Senior Member Join Date: Feb 2009 Location: Midwest USA Posts: 6,356 Blog Entries: 4

Electrolytics have tolerances as much as -50% to +100%

To make an affordable product, the use of 10% resistors is common.

The "Hard Part" is identifying which components need to be 1%, no matter what type of component. In an oscillator or amplifier, some capacitors can be off by double with no adverse effect, others can be off by 10% and it will function poorly.
#8
04-01-2009, 08:22 AM
 Kyuman New Member Join Date: Mar 2009 Posts: 5

Thanks Guys, that helps clarify the answer for me

 Tags capacitors, capaictors, explain, resistors

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