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  #1  
Old 03-31-2009, 11:16 AM
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Default 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?
2. Explain your answer

I have no idea how to approach this, can anyone help?
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Old 03-31-2009, 12:20 PM
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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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Old 03-31-2009, 03:36 PM
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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.
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Old 03-31-2009, 08:17 PM
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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...
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Old 03-31-2009, 09:17 PM
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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?
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Old 03-31-2009, 09:27 PM
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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.
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Old 03-31-2009, 11:59 PM
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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.
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Old 04-01-2009, 08:22 AM
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Thanks Guys, that helps clarify the answer for me
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