Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Suggestion on Transistors

  1. Dec 11, 2009 #1
    Hello everybody,
    I have an application which needs a pulse input ranging from +15v to -3v operating at 17.5 Mhz. The load capacitor is 150pF and the required rise and fall time of the pulse is 10nS. I am building a circuit with BJT's (both NPN and PNP) . I need some idea about the criteria for selection of BJT's available in the market.

    Can somebody suggest some available NPN and PNP transistors which work in this range.
    Also i tried searching for some RF transistors, but i was not sure if they are capable of handling such huge loads. The max collector current for RF transistors was around 50mA. I was not whether its possible to get such a strict rise/fall time with the given load. Can somebody comment on this calculations.

    Also any other suggestion or reference links are also welcomed.

  2. jcsd
  3. Dec 12, 2009 #2
    I used to use a 2N5770 npn for 1-2 ns risetime pulses, but it was only about a 0.75 volt to 1.5 volt pulse into 50 ohms. Are you talking about a pulse that goes from 15 volts to -3 volts? Into what impedance? To get the fastest pulses, always keep the transisitor conducting, but never in saturation.
    Bob S
  4. Dec 13, 2009 #3
    What is your application? Electro-optic modulator? Polarisation scrambler maybe?
  5. Dec 14, 2009 #4
    Image Sensor Driver
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook