suppose there is 0.5V peak to peak square wave, how is it possible to make it become a 3V pk to pk square wave?

 

Use an op amp with a voltage gain of 6. Here is some reference material - http://www.allaboutcircuits.com/vol_3/chpt_8/6.html.

 

Yes, as beenthere said, you can use a non-inverting opamp circuit to do this. The non-inverting configuration will not load your input signal, even if it is really high impedance.

The only real considerations you need to ensure are: make sure your opamp's output can swing to +/-3V (Should be okay with +-5V supply rails), make sure your slew-rate of your opamp is adequate (impossible to get a true square wave), and ensure that your opamp can handle the load you are driving.

Steve

 

Don't forget that your op-amp has to have enough bandwidth. Do not expect a 100kHz square wave to be reproduced with a gain bandwidth product of 200 kHz.