There is the following example:
simulate this circuit – Schematic created using CircuitLab
Its loading of the feedback network on the input side is 40kohm in series. Its loading of feedback network on the output side is 2kohm in parallel.
There is another example:
Frankly speaking, they are all from my exercise booklet, But the material related to this concept is really rare.
What is the definition of "the loading of feedback network on the input/output side", and how to analyze it?
It means what kind of load does the input of the circuit presents to the signal source, and what kind of load does the op-amp output has to drive, including both the intended load and the feedback network.
For an ideal model of an Op Amp we can neglect the input bias current and with negative feedback the differential input voltage will be forced to zero when the levels are in the "normal linear operating range".
Thus to measure signal input impedance or resistance which is the inverse to load current you know that Ri=Vi/Ii. The only signal current from the input signal, Vin, passes through the two resistors between Vi and Vo in the 1st example.
Both V+,V- op Amp inputs will be at 0V for the 1st inverting amplifier but the 2nd , both inputs will follow the signal Vi.
How does that change the signal load?
In 1) the input load is R1 and in 2) there can be no current flowing thru the input as the follower tracks the input so there is no input load.
The output currents are also slightly different. How does that change the voltage gain? (ignore RL for now)
You need to understand the concept of a virtual earth but, for now, the inverting input is a virtual earth: -
So, the inverting input node, as far as the output is concerned might as well be connected to real 0 volts and that means that R2 (40 kohm) appears as the output load.
And, as far as the input (Vi) is concerned it is loaded by 2 kohm.
This happens because the op-amp can be regarded as having near-infinite gain and this means that the two inputs (+ and -) can be regarded as being at the same voltage and, given that the non-inverting input is set at 0 volts, the inverting input must also be at 0 volts (due to negative feedback).
I believe that in this context, "loading" is referring to whether or not the source of input signal is required to sink or source current.
In this schematic I use red arrows to indicate the flow of current, in/out of the op-amp output to/from wherever it goes:
simulate this circuit – Schematic created using CircuitLab
In the inverting arrangement (top), output current is required to be sourced/sunk by the input voltage source.
For the non-inverting amplifier (bottom), the input voltage source is completely unloaded, since all output current is sourced/sunk from/to ground.
I imagine that "loading on the input side" refers to what's happening in the top, inverting configuration.
