supply voltage= +5 and -5
we are testing the op amp on breadboard.
for testing purpose we are utilizing standard frequency generator in lab not ad9833.
after 200 kHz distortion starts at the peak and then it attenuate and reaches 2.64 volts at 1 MHz.
I made a buffer using op 37 with AD 9833 input(600mV pk-pk ,300mV dc offset) and found that output starts attenuating at 200 kHz.
i found that as i change frequency from 0 to 200K, the inverting and non inverting pins showed same waveforms. but the moment , i increase frequency above 200KHz, the waveform at inverting terminal shows distortion. and so is the output.. what is the characteristic of opamps that i have to look for to understand this behavior.
also, i observed one more thing related to output voltage swing vs frequency in the datasheet. Please refer fig.TPC20 on page no.9 of Op37. the output swing reduces above 200Khz. will that be a reason of my problem.
Also, i tested opamp in buffer config. in that using input voltage of 0.6V from a std. function gen, i got output at all the frequencies whereas voltage of 4V from a std. function gen showed same problems after 200KHz.
I have taken a look at the simulation that u did. Will u pls tell me the reason for connecting R3 and R4 in the circuit diagram.
the waveforms were surprising although. at 100Khz, it showed clipping and 500Khz , it showed a decent sinewave. whats is slew rate distortion? and why the shape of sinewave improve after 100KHz?
Again, i would appreciate the time and effort u put in doing these things and giving valuable suggestions about ad8029,LT318!!!!
also, let me know about the simulation software u used. is it equipped with all the ICs like op37 etc?
but i need a proper flat response till 9MHz. so this is a boundry condition since i dont know as when voltage starts falling since datasheet shows open loop gain.
last but not the least- i m going thru types of opamp voltage feedback, current feedback and rail to rail. but not quite understanding rail to rail. will u pls explain me in short what do u mean by rail to rail. also, how to frame an application depending upon the type of opamp(voltage feedback,current feedback,rail to rail)?
You may be running into slew-rate limiting. The OP37 has a maximum slew-rate of 17V/µs. The maximum slew rate of a sine-wave is 2Π*f*Vp where f is the frequency and Vp is the sine-wave peak voltage. From this the maximum peak sine-wave voltage at 1MHz is 2.7V.
The capacitance at the op amp inverting (-) junction is critical, so minimize that by keeping all connections (resistor leads, etc.) to that point as short as possible.
Now, i increased input freq to 470KHz and I got 5V output as indicated in 2nd post. It is a significant increase in the amplitude and are you able to interpret the reason for that. If so, please let me know about it. And after 550-600KHz, the waveform was not sinewave as u indicated (slewrate limitation) in the figures. "
I am doing this testing because, such sudden voltage amplification should not occur with other opamp and trying to understand the reason behind it. If, the reason is understood, either the circuit can be adjusted for my application or an opamp can be selected properly.
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