switch a LED with a MOSFET

[andoo2012]

Hello,
I am working on a project where I need to turn a LED on/off by an FPGA pin (1.8V). It needs to work with up to 50 Mhz frequency.  I am currently using a channel MOSFET(BSS138PW) but the switching is very slow. The schematic pic is attached. The gate capacitance might be too high for FET to switch efficiently. Can I use a buffer before MOSFET to solve this problem? are there other better parts that I can use? Could somebody please point me to any articles/videos related to this topic?

[Nikan]

I think your mosfet is too slow to handle 50mhz, could be more on the max side of the datasheet...
Having a 0Ohm gate resistance can destroy your fpga.
Try a generic 100mhz bjt with the correct base resistor.

If it's not the fet, a buffer would only help if the fpga can't supply enough current to charge/discharge the capacitance at that switching rate. Duty cycle should be considered as well.

If you don't have to use a discrete component you could also use something like the NC7WZ14 to directly drive the led.

[Wolfram]

In a common-emitter (source) configuration, a BJT will likely switch even slower due to storage time. The other suggestion of using an NC7WZ14 or any other modern fast gate (74LVC1G14, etc.) is more likely to do what you want. If you need more current than can be provided by a single gate, multiple can be paralleled through current sharing resistors, which can also serve the role as current limiting for the LED.

[Terry Bites]

MAX3966/7 for instance?

[exe]

Why do you need to switch the led so fast? Is it a laser or something?