# Converting a fast-switching 0-2.5V input to TTL signal

Dear fellow engineers,

I am attemping to convert a fast switching (~ns) 0V - 2.5V pulse from FPGA into a TTL-standard (0V - 5V) signal. I have been browsing for voltage regulators online. Most of them seems to do the job in terms of stepping up the voltage, but their maximum switching frequencies are all too low. I would love to hear your advice on how to achieve this.

For completeness of the context, the purpose of this task is to send the FPGA-controlled fast-switching signal into a laser driver which only accepts TTL signal. The FPGA's maximum output is 2.5V which would not meet the standard.

• TTL threshold is 0.8 to 2.0V, what's wrong with that? Oct 4 at 19:18
• Voltage regulators produce a constant DC voltage (e.g. 12V or 5V), usually as part of a power supply. They cannot convert logic signals. You're looking for a level shifter. Oct 4 at 19:34
• High speed op-amp or comparator, step-up transformer. Oct 4 at 23:12

It sounds like you want a level shifter for logic signals; by which I mean relatively low output current source/sink for TTL 5V signal.

Taking the example from Texas Instruments their Voltage translators & level shifters overview page provides the following selection table which shows the capabilities of voltage level translation and data rates:

• That makes sense! Though I didn't think of a level shifter because I somehow didn't get into the idea of using that shifter "digital output" for an analogue input, but I do believe that this should work. Thank you! Oct 4 at 18:52

I am attempting to convert a fast switching (~ns) 0V - 2.5V pulse from FPGA into a TTL-standard (0V - 5V) signal.

Well, it might just work without any conversion. Look at the diagram below from here: -

On the left it shows that a TTL input can work with a logic high input level as low as 2.0 volts. Obviously, if your signal feeds the pin directly at 2.5 volts then it is likely to work. Anyway, for a TTL output, the minimum level that logic 1 can be is specified as 2.7 volts and your signal is a little bit light of this value. Nevertheless, if you only need to feed this signal to a single TTL-compatible input, it will likely work.

• The input, despite being TTL, was further described to require higher than 2.6V as an input - hi, and that's why I decided to lift it up a bit just to make sure it can be recognized. Though I think it's worth trying just 2.5V in case it works. Thank you for the answer!! Oct 4 at 18:55
• It cannot be described as TTL if it needs at least 2.6 volts Oct 4 at 19:02