Regarding inverting my analog signal.

crutschow

Joined Mar 14, 2008
38,745
Below is the LTspice simulation:
I used one of the rail-rail op amps available in LTspice, but just about any RR op amp should work.
The U2 pot is to tweak the offset to compensate for component and supply voltage tolerances.

I attached the .asc file, which you can simulate by clicking on it.

1580324872801.png
 

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Analog Ground

Joined Apr 24, 2019
460
This circuit shows a limitation of using a single power supply. A single supply forces the offset signal to the non-inverting input. Because of this, the offset is a function of the input signals source impedance or, in other words, the non-inverting gain depends on the source impedance. Also, if the input source is disconnected, the offset shifts down a lot.

Of course, these concerns are completely application dependent. The source impedance may be very low and it may not matter if the source is disconnected and the output shifts. Dual power supplies would allow the offset circuit to attached to the inverting input and both of these potential issues go away. Any ideas how to shift the offset to the other input when using a single power supply?

Also, an improvement would be to put in a +2.5V voltage reference for the offset. Good to eliminate a source of drift and noise. Again, application dependent how much precision and stability is required.
 

Analog Ground

Joined Apr 24, 2019
460
If that's a problem then a non-inverting buffer/follower can be added at the sensor output, of course.
Many op amps (although not this particular one) come in a dual or quad package, so doing that won't require an increase in part's count.
and a resistor to ground on the non-inverting input of the follower to keep things tidy if the input signal is disconnected.
 

Thread Starter

Dinesh_rd7

Joined Jan 26, 2020
43
This circuit shows a limitation of using a single power supply. A single supply forces the offset signal to the non-inverting input. Because of this, the offset is a function of the input signals source impedance or, in other words, the non-inverting gain depends on the source impedance. Also, if the input source is disconnected, the offset shifts down a lot.

Of course, these concerns are completely application dependent. The source impedance may be very low and it may not matter if the source is disconnected and the output shifts. Dual power supplies would allow the offset circuit to attached to the inverting input and both of these potential issues go away. Any ideas how to shift the offset to the other input when using a single power supply?

Also, an improvement would be to put in a +2.5V voltage reference for the offset. Good to eliminate a source of drift and noise. Again, application dependent how much precision and stability is required.
I can't understand the thing that u said
 

ericgibbs

Joined Jan 29, 2010
21,554
hi D,
It means add a resistor from the Vinp to 0v, say 47k or so. [ Across V1 ]
If the Sensor is disconnected for any reason the Vinp does not 'float' [ not connected]
OK.
E
 

crutschow

Joined Mar 14, 2008
38,745
The circuit is configured correctly except R12 should be 10k also.
What are the supply voltages for the opamp?

I asked for the simulation results so where are they?
What do the input and output signals look like?
 
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