How to increase fanout of CMOS buffer

Discussion in 'The Projects Forum' started by Prakash Scientist, Jun 22, 2016.

  1. Prakash Scientist

    Thread Starter New Member

    Dec 19, 2012
    I'm new to online forum. I want to interface 74HC541(Buffer) to 74HC574(D-f/f). The thing is 100's of D-f/f parallel interface as shown in figure(Fig.1).
    Input and load capacitance limits it to 10 to 15 fanout. Fanout of buffer current wants to charge input capacitance of D-f/f. So increasing D-f/f increases charge time of input capacitance.
    My question is this can be overcome by giving more current to increase charge current to input capacitance by adding pull up resistor to input of D-f/f(Fig.2) or BJT emitter follower(Fig.3).
    This would correct or not...

    Thanks in advance...
    Last edited by a moderator: Jun 22, 2016
  2. MrChips


    Oct 2, 2009
    Prakash Scientist likes this.
  3. kubeek


    Sep 20, 2005
    use more buffers to divide the signal into branches that feed other buffers untill you have enough fanout to drive all the FFs. If the first stage drives 15 buffers, and those each drive 15 FFs, you get 225 FFs alltogether.

    (Or use an FPGA to do the logic, instead of driving hundreds of ICs, but that really depends on what the design is for...)
    Prakash Scientist likes this.
  4. Prakash Scientist

    Thread Starter New Member

    Dec 19, 2012
    Thanks for your valuable suggestion and from your suggestion I go for buffer tree.:)