Hi,
This is my first post.
Also not very experienced as electronics student as well.
_____
I need to make a circuit to drive some IR Leds for a project.
IR Leds needed to be able to pulse at least @ 10Mhz.
So far, I have made this design:
----
Op-amp= AD8056 (Voltage feedback, 300 Mhz, high slew rate, etc.)
Vin=3.2Vp-p square wave (from a signal generator)
R3= 402Ω
R2= 402Ω (recommended resistor values for a GAIN=2)
R1= 10Ω
C1=C3=C5= 0.1μF
C2=C4=C6= 1μF (added for stability at high freq.)
IR Leds= OPE5685
(http://www.analog.com/static/imported-files/data_sheets/AD8055_8056.pdf)
----
My problems are:
> @ 5Mhz I am getting an optical signal (from Leds) square wave (good) but with a little delay (bad),
> @ 10Mhz the optical signal is not a square wave any more (bad)
> Also, when I connect the input signal (from signal generator) to my circuit, the input signal (as seen on the oscilloscope) become noisy.
Vin and Optical signal @ 10Mhz:
Yellow= Vin
Purple= Optical signal from IR Leds
I think the problem is not due to Leds.
The output of the ap-amp @ 10 Mhz is as shown below:
Blue= Output of the op-amp (transistor base).
I have tried:
> several gains,
> a faster op-amp,
> the circuit is on a breadboard but I have tried also on a stripboard (the final circuit will be on a PCB, hopefully),
> to reduce Vin to a lower voltage,
> ++
but the result is almost the same,
To conclude:
> Up to 2 Mhz working fine,
> 2~5Mhz square wave but with delay,
> 5+ not any more square wave, delay, noise, etc.
Any help is much appreciated
This is my first post.
Also not very experienced as electronics student as well.
_____
I need to make a circuit to drive some IR Leds for a project.
IR Leds needed to be able to pulse at least @ 10Mhz.
So far, I have made this design:
----
Op-amp= AD8056 (Voltage feedback, 300 Mhz, high slew rate, etc.)
Vin=3.2Vp-p square wave (from a signal generator)
R3= 402Ω
R2= 402Ω (recommended resistor values for a GAIN=2)
R1= 10Ω
C1=C3=C5= 0.1μF
C2=C4=C6= 1μF (added for stability at high freq.)
IR Leds= OPE5685
(http://www.analog.com/static/imported-files/data_sheets/AD8055_8056.pdf)
----
My problems are:
> @ 5Mhz I am getting an optical signal (from Leds) square wave (good) but with a little delay (bad),
> @ 10Mhz the optical signal is not a square wave any more (bad)
> Also, when I connect the input signal (from signal generator) to my circuit, the input signal (as seen on the oscilloscope) become noisy.
Vin and Optical signal @ 10Mhz:
Yellow= Vin
Purple= Optical signal from IR Leds
I think the problem is not due to Leds.
The output of the ap-amp @ 10 Mhz is as shown below:
Blue= Output of the op-amp (transistor base).
I have tried:
> several gains,
> a faster op-amp,
> the circuit is on a breadboard but I have tried also on a stripboard (the final circuit will be on a PCB, hopefully),
> to reduce Vin to a lower voltage,
> ++
but the result is almost the same,
To conclude:
> Up to 2 Mhz working fine,
> 2~5Mhz square wave but with delay,
> 5+ not any more square wave, delay, noise, etc.
Any help is much appreciated