# How to explain? Resistors and Capacitors

Discussion in 'Homework Help' started by Kyuman, Mar 31, 2009.

1. ### Kyuman Thread Starter New Member

Mar 31, 2009
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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. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
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.

3. ### mik3 Senior Member

Feb 4, 2008
4,846
63
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. ### kakin New Member

Mar 24, 2009
9
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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. ### Kyuman Thread Starter New Member

Mar 31, 2009
5
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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. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
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.

7. ### thatoneguy AAC Fanatic!

Feb 19, 2009
6,357
718
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. ### Kyuman Thread Starter New Member

Mar 31, 2009
5
0
Thanks Guys, that helps clarify the answer for me