Components on the back of CPU

Discussion in 'Embedded Systems and Microcontrollers' started by Shagas, Sep 4, 2015.

  1. Shagas

    Thread Starter Active Member

    May 13, 2013
    802
    74
    Hello

    I've been wondering for quite some time at what those components on the back of desktop CPUs are. I've tried
    googling many times with no success.

    [​IMG]


    Perhaps decoupling caps? But then why so few and why on board when you can put them right beneath the cpu on the MB.
    My second guess is thermistors, but I still can't figure out what those 8-pin packages are. Resistors? If so then what for.
    Thanks in advance
     
  2. ISB123

    Well-Known Member

    May 21, 2014
    1,239
    527
    That is just a RC filter.
     
  3. OhmsOutlaw

    New Member

    Sep 4, 2015
    8
    1
    Big components are capacitors (not RC filters) used for locally decoupling specific power domains in the processor core. The smaller IC looking components are ESD filters. you usually places those close to a high speed signal source. Common mode filters are used for differential signals and TVS diode filters are used for single ended signals.
     
  4. Shagas

    Thread Starter Active Member

    May 13, 2013
    802
    74
    Is it really necessary to have the decoupling on the processor itself or did they just do that not to rely on motherboard manufacturers to place
    the caps?

    What are the ESD filters for? User mishandling or are there other sources that might damage the processor?
     
  5. OhmsOutlaw

    New Member

    Sep 4, 2015
    8
    1
    It is common practice to have local power decoupling for any high-end device. It is important to place the cap close to the load because this makes the power available immediately and the voltage drop associate with the DC resistance of the power plane / trace is minimized. On some of the newer processors the capacitance can be build into the PCB, which may eliminate the need for external caps. The faster the processor, the more power it will draw due to increases in switching frequencies so the more need there is for a local cap.

    As far as the ESD filter goes, adding one to high speed traces will both help protect the the traces from external sources (clocks, other high speed signals, etc) and will also help keep the board more "quiet". These types of filters are typically used on DDR, HDMI, PCIe, USB, etc. So the use for the ESD filter here is not to prevent damage but to minimize trace-to-trace coupling and prevent things like double-clocking, ringing or insufficiently high / low logic levels.
     
    Shagas likes this.
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