i have a problem with finding the right components and circuit for the following problem.

I have a device that is producing trigger signals with a length of 100 ns at a amplitude of 1.8 V (left part of the picture). To trigger a RF-Switch it is necassary to shift the 1.8 V to a 5 V signal (TTL). The circuit have to operate only in one direction but really fast. The delay between the trigger signal and the amplified signal should be less than 5 ns (if possible!).

problem description

I am not sure which option is the best solution for this problem. Should i use a CMOS or a set of bipolar junction transistor. Do you know components that have a low raise and delay time for this application? Thank you in advance

  • 3
    \$\begingroup\$ For an integrated 'one-chip' solution your best bet is a sn74lvc1t45 (see table 7.6 in datasheet), depending on your load capacitance and switch voltage levels (table 7.6 uses section 8 loading for the propagation times, so your case may be better). Otherwise you're going to be designing a non-saturating BJT switch, which would have faster transitions and prop delay, but will take some more design effort (don't know what your critical path is). \$\endgroup\$ – isdi Nov 13 '18 at 0:40
  • \$\begingroup\$ Thank you for the response. I think the non-saturating BJT switch is a good option. Do you have a specific BJT in mind? It is also possible to use a CMOS switch with less then 10 ns rise time? \$\endgroup\$ – REMberry Nov 13 '18 at 8:05
  • \$\begingroup\$ Not at the moment, perhaps there is a misread here, rise time and propagation delay are two different things. Getting a rise time of <10ns is relatively easy, propagation delay is more difficult. \$\endgroup\$ – isdi Nov 13 '18 at 13:50
  • \$\begingroup\$ Why then not choosing a MOSFET? They basically should have a higher bandwidth, right? \$\endgroup\$ – REMberry Nov 13 '18 at 19:29
  • \$\begingroup\$ (MOS)FETs tend to have rather large gate capacitance, so you have to look at your source to see what it's happy with. You would need to find a FET whose Vgs threshold is around 1.8V (or lower). A JFET would be a better choice if you go this route, but the selection is more limited. In any event if you go with a discrete solution you are also dealing with layout and package parasitics. You could look into using an SN74F244 buffer and paralleling the inputs and outputs to get better load drive capabilities, you would have to pull up the inputs to get the 2.0V minimum high. \$\endgroup\$ – isdi Nov 13 '18 at 23:04

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