OpAmp voltage join

The use of T/Y feedback network allows the use of three lower resistances instead of single very high resistance. The need for this configuration arises when there is a requirement for a large gain and a minimum input impedance. These requirements can result to a very large feedback resistance, if this feedback resistance is impractical the designer will resort to the T/Y feedback. The parameters in this example may not be compelling enough for a designer to opt for the T/Y feedback network but it serves to illustrate the concept. The output in the circuit is ideally -12 V, the gain is -60 so it would have required a single 600 kOhms resistor.