Arduino Pulse Generator LVTTL/TTL

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1

I'm trying to set up a pulse generator to generate short LVTTL/TTL pulses with an Arduino. Since I'm pretty much an electronics beginner, I need some help setting up the circuit. The Arduino pulses shall send a start trigger signal to a digital timing device that only accepts LLTTL/TTL signals at a BNC 50 ohm input.

I know that the Arduino digital pins do not supply enough current to send the start trigger signal to the 50 ohm BNC port of the timing device. I did some research and read that a MOSFET could be a way to solve that problem. Unfortunately, I am slightly lost which MOSFET to choose for this application and how to set up the circuit in general.

Can anyone give me some advice on how to pursue? Thanks a lot!

2

  • Not sure what exactly you are trying to do, if you are wanting to select a MOSFET to be switched by an Arduino (ex. UNO) look for a logic level MOSFET (can be controlled by 5v logic).

  • These are some of the MOSFETS that fit this category.

3

Does the device that requires the trigger pulse actually have a 50Ω terminating resistor at it's input?

... or does it merely use a '50Ω BNC connector' to make connections to a high resistance input?
If it is the latter, then you can simply make a direct connection.

For instance:
I know that my Function/Arbitrary Waveform Generator uses a BNC connector for its trigger input, but has a 100kΩ input impedance, and I can trigger it from an Arduino pin.

Trigger input
Trigger input937×225 14.4 KB

Check the manual of your device needing the trigger signal to find out what it's input impedance is.

4

You need a 50 Ohm driver that accepts TTL input signal levels - or the like.

5

Or better post details of your timing device so we can look up its specifications and figure out what will work.

6

Thanks to everyone who replied to my post. The timing device is a Digital-to-Time Converter by Surface Concept (SC-TDC 1100 S-Series). The manual specifies "that all inputs are internally 50 ohm terminated and are laid out for 50 ohm terminated LVTTL signal levels".

7

Use Ohm's law and find out that these voltages on 50 Ohm require line drivers capable of the resulting currents.

8

For a LVTTL signal the high logic level should have at least 2.4 V. I assume against the 50 ohm resistor I need a line driver with around 48 mA output current, better more. I've found the SN74ACT244, but the absolute maximum continuous output current is only +/- 50 mA. I didn't find a better alternative yet. Would it be possible to use two outputs of the SN74ACT244 and switch the outputs in parallel?

9

You'll find 50 Ohm devices in the analog SN75... series.