I implemented a simple voltage follower circuit using OP-07 OPAMP. It follows the input volts of 0 to 5 V sine wave upto 10 kHz, but if i increase the frequency from signal generator beyond 10 kHz the waveform gets distorted, it becomes something like triangular wave. Also to work beyong 10 kHz faithfully, i need to reduce the input sine amplitude below 5 Volts. I don't understand what is the issue.
I guess there is some issue with my signal generator cable. I attached the pic of my signal generator cable, and the circuit diagram also.

Regards,
Abhishek

 

Hello,

The large signal properties will play part in your system:



At higher frequencies the maximum swing will drop drasitcaly.

Bertus

 

Hello,

The large signal properties will play part in your system:

View attachment 121126

At higher frequencies the maximum swing will drop drasitcaly.

Bertus

Bertus, thanks for your support. I doubt that i need proper connection at breadboard side, so that there is no stray capacitance issue. What is the proper way to connect the generator output to my breadboard or PCB so that it may be terminated properly.

 

Hello,

10 kHz will not be to much for a breadboard.
It is the speed limitation of the opamp that will give the distortion you see.

Bertus

 

I implemented a simple voltage follower circuit using OP-07 OPAMP. It follows the input volts of 0 to 5 V sine wave upto 10 kHz, but if i increase the frequency from signal generator beyond 10 kHz the waveform gets distorted, it becomes something like triangular wave. Also to work beyong 10 kHz faithfully, i need to reduce the input sine amplitude below 5 Volts. I don't understand what is the issue.
I guess there is some issue with my signal generator cable. I attached the pic of my signal generator cable, and the circuit diagram also.

There is nothing wrong with your circuit, your breadboard or your cable. The reason you're seeing this distortion is that your OP-07 is slew rate limiting; that is, there is a limit to how fast the op amp's output voltage can change. From the data sheet (see attachment on post #2), the OP-07 has a maximum slew rate of approximately 0.3 volts/μs. A sine wave has a peak dv/dt of π ⋅ f ⋅ V, where V is the peak voltage of the sine wave, so at 10 kHz and 5 volts, your input signal has a peak dv/dt of 314000 volts per second, or 0.314 v/μs. At higher frequencies, your voltage follower simply isn't fast enough to faithfully follow your input signal.

The bottom line is, you need to use a faster op amp.

 

There is nothing wrong with your circuit, your breadboard or your cable. The reason you're seeing this distortion is that your OP-07 is slew rate limiting; that is, there is a limit to how fast the op amp's output voltage can change. From the data sheet (see attachment on post #2), the OP-07 has a maximum slew rate of approximately 0.3 volts/μs. A sine wave has a peak dv/dt of π ⋅ f ⋅ V, where V is the peak voltage of the sine wave, so at 10 kHz and 5 volts, your input signal has a peak dv/dt of 314000 volts per second, or 0.314 v/μs. At higher frequencies, your voltage follower simply isn't fast enough to faithfully follow your input signal.

The bottom line is, you need to use a faster op amp.

Thank you sir for ur support. We are working here in smps power supply control job. So the signal frequency is around 10 kHz range only. I m actually designing optocoupler circuit using opamp and IL300 optocoupler. The circuit diagram is attached. O/P should follow input signal, but it shows a noisy sine wave at o/p at low signal levels below 1Volts. Pls help me, i need to couple the signal to my fpga board.
I need to couple a unipolar signal frm 0 to 2V atleast.

 

The circuit diagram is attached.

Please draw a proper schematic; one that doesn't require anyone reading it to have to look up the pinout for the IL300 before they can analyze the circuit.

 

We are working here in smps power supply control job. So the signal frequency is around 10 kHz range only.

If you expect to accurately couple a complex waveform, you MUST use a faster op amp that can respond not just to your 10 kHz fundamental frequency, but its harmonics as well.

I m actually designing optocoupler circuit using opamp and IL300 optocoupler. The circuit diagram is attached. O/P should follow input signal, but it shows a noisy sine wave at o/p at low signal levels below 1Volts. Pls help me, i need to couple the signal to my fpga board. I need to couple a unipolar signal frm 0 to 2V atleast.

First, your diagram shows no connection to pin 1 of the IL300; it should be connected to Vcc. With pin 1 open, you'll get no coupling at all.

And second, you need to calculate appropriate resistance values for R1 and R4 based on the servo gain (K1) and the forward gain (K2) of the IL300. If your resistances are too low, you won't get much output.

 

Here's the schematic from the data sheet showing the innards.
Pin 1 needs to connected to ground.
And, as has been noted, you need a faster op amp.

 

If you expect to accurately couple a complex waveform, you MUST use a faster op amp that can respond not just to your 10 kHz fundamental frequency, but its harmonics as well.


First, your diagram shows no connection to pin 1 of the IL300; it should be connected to Vcc. With pin 1 open, you'll get no coupling at all.

And second, you need to calculate appropriate resistance values for R1 and R4 based on the servo gain (K1) and the forward gain (K2) of the IL300. If your resistances are too low, you won't get much output.

Thank u sir. I forgot the gnd connection in the schematic, but actually it was there. So finally i need to use faster opamp i.e. with faster slew rate than OP07, but can u pls tell why u recommended to use high resistors. I used 10k resistors in circuit. I found the distortion in my signal at low amplitude levels.

 

So finally i need to use faster opamp i.e. with faster slew rate than OP07...

You might consider using an LT1007, which is about 10X faster than an OP07 while maintaining the OP07's DC accuracy and low noise.

...but can u pls tell why u recommended to use high resistors. I used 10k resistors in circuit. I found the distortion in my signal at low amplitude levels.

I'm not recommending higher value resistors specifically, just noting that the resistor values should be calculated based on K1, K2 and the desired operating current for the IL300's LED.