How to amplify a signal to trigger a function generator

amplifierfunction generatoroperational-amplifier

I have two digital signals, I perform a AND operation on these two signal with an AND gate (TI SN74LS08N), and want to use the output signal to trigger a function generator which will generate another signal.

So I did get the AND signal from the gate, and when I connect the output signal from AND gate to the oscilloscope, the signal looks good and have 0 and 5V for low and high. But when I connect this signal to the function generator, and put the generator to external trigger mode, the function generator is not triggered. I used the oscilloscope to check this signal, and found when the function generator is connected, the output signal from the AND gate dropped to 0 and 500mV for low and high, which is absolutely not enough to trigger the function generator.

So my question is how to amplify this output signal from AND gate so that it is enough to trigger the function generator? Can I use an op-amp to amplify the signal?

If so, how can I do it? One thing I am thinking is if I use the op-amp, how should I choose the resistor ratio to get the proper gain? I mean, before I connect the output from AND gate to the function generator, the signal is 5V for high, only after I connect it to the function generator, it drops, so should I use the dropped signal, for example, 500mV to calculate the gain, which will be 10?

================

Update:

The function generator is a DEI PDG-2515, the data sheet can be found here.

Best Answer

Going purely by the (somewhat unlikely) results of connecting the trigger input, as reported in the question:

The problem is not a low output signal from the gate itself, but a lack of external pull-up resistor at the output. Note that the datasheet indicates an output current sink rating of 16 mA, but source rating of only -0.4 to -0.8 mA.

Add a pull-up resistor of around 1 kOhms from the output of the gate to Vcc, and the output should trigger the signal generator fine.

Related Topic