plus or minus unity gain

32 This unity gain amplifier is capable of producing an inverted or a non- inverted output signal, as required, depending on the voltage level present at the control input (A). The circuit works in a very simple manner. If the control input voltage is 0 V, the non-inverting input of the opamp (pin 3) will be connected to earth by way of the conducting FET. The opamp is now connected as an inverting amplifier causing the inverting input to constitute a virtual earth point (the opamp maintains the voltage level at pin 2 equal to that at pin 3, in this instance, ground). With the given values for R1 and R2 the gain will be —1. If the control input (A) is connected to —Ub the FET will turn off and will form a high impedance load for the rest of the circuit. Now the out- put of the opamp will not be inverted but the gain will remain the same. The input level must remain plus or minus unity gain Uin within 2 volts of the supply voltage extremes, (thus, Vb + 2 V < Vib < + Vb —2 V)....