How to explain? Resistors and Capacitors

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

  1. Kyuman

    Kyuman Thread Starter New Member

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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?
    2. Explain your answer

    I have no idea how to approach this, can anyone help?
     
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  2. Wendy

    Wendy Moderator

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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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  3. mik3

    mik3 Senior Member

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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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  4. kakin

    kakin New Member

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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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  5. Kyuman

    Kyuman Thread Starter New Member

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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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  6. Wendy

    Wendy Moderator

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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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  7. thatoneguy

    thatoneguy AAC Fanatic!

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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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  8. Kyuman

    Kyuman Thread Starter New Member

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    Thanks Guys, that helps clarify the answer for me
     
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