Switching digital signal

Discussion in 'The Projects Forum' started by sezo, Nov 20, 2012.

  1. sezo

    Thread Starter New Member

    Nov 19, 2012
    Hi to everybody,

    I am on a project where I have to switch a wire to ground or 12V. The signal on the wire is a +-1V digital signal (rectangular with max. ~27MHz frequency) . The task is to find a switching solution to take the wire down to ground, to 12v or doing nothing ( not inteferring with the signal/ high impedance). The Control signal to turn the switch on/off comes from a uC.

    That is why I thought about a Tri-State Buffer like CD4503BE.The switch has to be fast (>50MHz) because i need to be faster than the digital signal. But the one above and some other are all not fast enough ( Transition/propagation times are all to high >40ns).

    Do you have another solution in mind?

    I also tried analog switches like HEF4050, but it switches at 4.5V so i have to shift the level up of the wire. The next try will be the HCF4066BE with control input.

    Another idea would be with FETs as switches like the attached picture from here
    Would be glad to receive some help.
    Thank you very much
  2. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    What does it do?
    Why does it have to be >50MHz?
    Do you have any experience designing data and switching circuits that run >50MHz?
  3. sezo

    Thread Starter New Member

    Nov 19, 2012
    I have no experience with High speed switching circuits. Sorry it was a mistake the switching speed doesnt have to be >50MHz.

    I have tried to Simulate it now with bipolar transistors. It switches up to 50MHz, but I think 25MHz should be enough.

    I attached two files of the simulation, simulation tool is SIMetrix. If someone needs the files just mail me. The NPN is a BFG480 and the PNP a BFT92.

    Do you see anything to improve in the circuit?

    Thank you and greets