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?
  2. Bill_Marsden

    Bill_Marsden Moderator Staff Member

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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.
  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.
  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...
  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?
  6. Bill_Marsden

    Bill_Marsden Moderator Staff Member

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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.
  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.
  8. Kyuman

    Kyuman Thread Starter New Member

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    Thanks Guys, that helps clarify the answer for me
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