Hi,
I have a particular problem with an inverting op amp amplifier. I have a signal which is "sensitive" - sorry I'm not sure of the right term to use here.
I am using a HEXSense FET to detect the current in a stepper motor driver. I have read an application note which states that the "sensitive" sensing voltage of the FET should be amplified through use of a virtual ground op amp amplifier, which will obviously invert the polatiry of the signal (ie an inverting amplifier). My problem is that I need the output voltage from the amplifier to be of the same polarity as the input signal.
No problem I thought, I'll simply put the output of the inverting amplifier through a second, unity gain inverting amplifier to get it back to the same polarity (only amplified).
Rather than heat up the soldering iron, I decided to simulate the circuit in B2 Spice to see if it worked as I expected, but it doesn't. The trace from the B2 Spice Oscilloscope is attached, as is a jpeg of the circuit I am simulating.
In the circuit the signal generator provides a 1V peak to peak, centered around + 0.5V, 20 kHz square wave into the inverting input of the first op amp (the RED trace on the scope) and the output from the second op amp is the BLUE trace. The opamps are both TL084's.
I don't understand WHY this doesn't work. If anyone can shed any light on this I would be very appreciative.
Regards and thanks
Pete
I have a particular problem with an inverting op amp amplifier. I have a signal which is "sensitive" - sorry I'm not sure of the right term to use here.
I am using a HEXSense FET to detect the current in a stepper motor driver. I have read an application note which states that the "sensitive" sensing voltage of the FET should be amplified through use of a virtual ground op amp amplifier, which will obviously invert the polatiry of the signal (ie an inverting amplifier). My problem is that I need the output voltage from the amplifier to be of the same polarity as the input signal.
No problem I thought, I'll simply put the output of the inverting amplifier through a second, unity gain inverting amplifier to get it back to the same polarity (only amplified).
Rather than heat up the soldering iron, I decided to simulate the circuit in B2 Spice to see if it worked as I expected, but it doesn't. The trace from the B2 Spice Oscilloscope is attached, as is a jpeg of the circuit I am simulating.
In the circuit the signal generator provides a 1V peak to peak, centered around + 0.5V, 20 kHz square wave into the inverting input of the first op amp (the RED trace on the scope) and the output from the second op amp is the BLUE trace. The opamps are both TL084's.
I don't understand WHY this doesn't work. If anyone can shed any light on this I would be very appreciative.
Regards and thanks
Pete