I've got a sensor that outputs a .7Vpp square wave at 36kHz-60kHz. I need to take that square wave and amplify it to 5Vpp, as close to 0V to 5V rails as possible. Then I need to send that signal over a long cable, 6-50 feet depending on where I'm using the sensor and have that square wave still be nice and square when it reaches the other end.
I have a single +5VDC supply to work with.
Currently I can get a good square wave by using an LM311P comparator, but when I try to drive it over a long cable I end up with a wave that looks like a shark fin.
Should I be taking a different approach all together instead of the comparator, or is there something I can put between the comparator and the long cable to help the signal?
This is a little bit of a simplification of what I'm doing, but it's basically what I'm doing now. NOTE: the BJT shown is actually part of the LM311P comparator. Also, the 1V source is actually 5V.
simulate this circuit – Schematic created using CircuitLab
Here's the shark fin output at 36kHz, about 5Vpp, that I was describing:
Best Answer
The circuit you're using is able to drive the cable very quickly to the low level, but only pulls up slowly to the high level because R1 limits the current available to charge up the capacitance of the cable. The maximum current you're going to be sourcing into your cable is about 3.3 mA.
One solution is, instead of buffering with the Q1/R1 combination, use a buffer/driver IC such as SN74LVC1G126. This can supply up to 32 mA current either sourcing or sinking. You'll have to work out from your cable length and capacitance per foot whether that will give you adequate edge speeds for your application.