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Hello,
Hope everybody is in good health,
I am a bit new to this High speed amplifiers world, i have basic understanding of the devices. I am working on a university project, that requires me to build a modulating LED driver circuit - from what I have researched is that, it can be built with a high speed OP-AMP (transconductance amplifier, voltage to current converter)
It is to be used as a fiber optic transmitter, so the output of an LED which is a pigtail fiber will be connected to the fiber cable.
I am using a IR Led for the fiber optic transmission.
This IR LED has an operating/forward current of 40mA - 60mA and forward voltage of 1.2V - 1.7V
1. LED should be biased for sinusoidal modulation
2. Pulse width of the analog signal to be LED modulated will be 0.1 microsecond, 1 Mhz frequency
3. Will be modulated with sine wave of 25Mhz to 50Mhz.
I am following this design by Neil P. Albaugh -, the input to the circuit will be through a function generator but the OP-AMP he has used has a slow slew rate and from what I have studied is that, a slow slew rate op-amp for this project may not work.
also I have read on different datasheets in TI website, that there are transconductance amplifiers ... while Neil has used a non-transconductance amplifier, so this has made me a bit confused.
Can any engineers out there help me .... thanks a lot.
There are several kinds of amplifiers, many of which are open loop and are indeed transconductance amplifiers.
Operational Amplifiers, are designed to be used with feedback. Operational amplifiers come in two main varities, voltage feedback and current feedback. To a first approximation they function the same in closed loop conditions, so for many applications they can be interchanged.
I think your question is more general than voltage feedback vs current feedback, though. An Operational Amplifier can be set up as a voltage amplifier or a current amplifier or a transconductance amplifier by using the feedback network.
If you want better slew rate you could look at the LMH6609.
I have attached a more classic voltage to current circuit here:
This seminar may help.
http://seminar2.techonline.com/~texasinstruments/TI_dec1405/files/lobby.html