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Both the inverting amplifier and non-inverting amplifier use negative feedback. Both provide gain. But one inverts the signal while the other does not. How to know which one to use? Are there applications where only one of the two can be used (provides both positive and negative supplies exist)?
Is it true that single supply op amp can only create non-inverting amplifier?
There are a couple reasons (at least) for choosing a particular configuration:
If you need a high input impedance, then you are forced into a non-inverting configuration. This is commonly required in a buffering situation. An inverting configuration has an input impedance equal to the input resistor which may load the source circuit.
If you need a summing amplifier, then inverting is the way to go as the inverting input is the summing junction.
Is it true that single supply op amp can only create non-inverting amplifier?
No. With a DC offset (on the non-inverting input) you can have an inverting configuration although the input signal will need to be ac coupled under most circumstances.
There are some specific applications which require (a) non-inverting or (b) inverting gain stages. This is true - in particular - for active filters and harmonic oscillators.
Opamps with JFET inputs tend to have an input capacitance depending on the input voltage. In inverting configuration, both inputs are at ground potential (one by being connected to ground, the other by being a virtual ground). That gives comparatively constant capacitance on the inverting input. The non-inverting configuration follows the input signal, and a signal-dependent capacitance will lead to harmonic distortion unless the input is driven with a rather low impedance.
Just recently I read a warning about this in the data sheet for the OPA2134 while the data sheet for the OPA1642 explicitly mentions having stabilised input capacitance essentially independent of the input voltage.
Through both configurations - inverting and non-inverting, the same negative feedback idea is implemented as follows:
The input Vin and (part of) the output voltage Vout are compared by subtraction and the result is applied to the (differential) op-amp input so that the difference to be zeroed.
It is only in the method of subtraction - in the inverting configuration, it is implemented in a parallel manner and in the non-inverting one in a serial manner. This leads to significant differences in the properties of the two circuit solutions.
Configuration. In the inverting amplifier, the two voltages are of opposite polarity (referenced to ground) and summed through a R1-R2 resistor network. The output (difference) voltage is also referenced to ground and therefore no differential input is required (the unused op-amp non-inverting input is grounded). So an inverting amplifier can be made by an amplifier with a single ended input but it has to be supplied by a voltage with an opposite (to the input voltage) polarity. This means that if the input voltage is bipolar, the op-amp has to be split supplied.
Gain. It is exactly equal to the ratio of the two resistances (R2/R1) because the two voltages being compared are separate.
Input resistance. Looked at from the other side, inside the loop the two voltages are of the same direction, therefore they are summed. As a result, the current increases and the input resistance decreases (Miller effect). In other words, the op-amp output voltage neutralizes the voltage drop across the resistor R2 and only R1 is left to operate; so the circuit part after R1 can be thought as a short connection.
Configuration. In the non-inverting amplifier, the two voltages are of the same polarity (referenced to ground) but are connected in the opposite direction in the loop (- +, + - or + -, - +) so they are subtracted. The difference voltage is "floating" so an amplifier with differential input is required... but it can be single-supplied.
Gain is one unit greater than the ratio of the two resistances (R2/R1 +1) because the output voltage includes the input voltage within itself. If we use the voltage drop across R2 as an output voltage, then the gain would be exactly R2/R1 as in the inverting amplifier but the load would be floating.
Input resistance. Since the two voltages are subtracted, the current enormously decreases and the input resistance increases ("bootstrapping" effect). Seen from the input source side, the circuit is an open circuit.
I have illustrated these explanations by CircuitLab simulations in my answer to a similar question.
You must always connect both input terminals of an opamp to thought-out and considered points. What you connect them to determines what function the opamp will provide.
If you connect +ve to a ground, and -ve via a feedback impedance to the output terminal, you create a 'transimepdance amplifier'. Any current you now push into the -ve input must also be balanced by a current from the output terminal through the impedance. Use a feedback resistor to convert current to volts. Use a feedback capacitor to create an integrator. The gain will be inverting.
If you connect your input voltage to +ve, and the -ve to a fraction of the output voltage (create a fraction with a voltage divider to ground, usually resistors, but you could use other impedances or even a transformer), you create a non-inverting amplifier, where the gain is the reciprocal of the feedback voltage divider.
You can do more complicated things as well, but the two above are the basics.
Some arguments I haven't seen mentioned in other answers:
I made primarly an error in my schematic. I apologize. I am getting old.
Always simulate to being sure !
If unsure of inverting or not inverting for general use, this schematic is ok. for pcb. Simply add possibility of short input+ to gnd, and left of R5 or R8 also to gnd.
Drop of solder. R7 may be lower. R10 may be ommitted. This schematic here is for Gain -1 or +1.
For general use, draw the wires on pcb for using drop of solder (or a jumper) to choose your configuration. It is only a little trick when you use a pcb for testing.
