Clock signal of 4093

Discussion in 'Homework Help' started by Clue, Aug 11, 2007.

  1. Clue

    Thread Starter New Member

    Jun 2, 2007
    Hi, anyone can explain how the oscillator circuit work as the pic shown below and why need to connect with resistors and capacitor? Thanks.

  2. spar59

    Well-Known Member

    Aug 4, 2007
    Is this a true homework assignment and designed as a bit of a teaser?

    The circuit arrangement is very illogical in my opinion in that it uses 1 resistor and 1 or 2 gates more than necessary.

    The more common arrangement would be one gate with inputs tied together a capacitor from these to ground and a resistor from the inputs to the output, then you could connect the output of this gate to the input of a second gate purely for buffering purposes if wanted. A diode and extra resistor can be incorporated to create different charge and discharge paths if an asymetric duty cycle is required.

    Furthermore, unless I am mistaken, the circuit configuration results in a charge-pump circuit that will push the gate input voltages beyond the supply rail, which is something that should normally be avoided.

  3. beenthere

    Retired Moderator

    Apr 20, 2004
  4. Gadget

    Distinguished Member

    Jan 10, 2006
    Your both right.
    the 4093 is a quad Schmitt nand, and being a schmitt needs only 1 gate, 1 resistor and 1 cap for a basic oscillator.
    The circuit supplyed should work, as it does with the standard Nand, Nor and inverter gates, but why waste the gates on a schmitt......
  5. spar59

    Well-Known Member

    Aug 4, 2007
    Thanks 'beenthere' for the weblink - the great thing about forums is the sharing of knowledge. Having read the article it appears that the input clamp diodes will protect the device from the attempted swings beyond the supply rails, perhaps I should make use of their presence to get the most out of a device but I have an inbuilt reluctance to rely on them (perhaps I should stop being paranoid). The article answers the initial question perfectly.