What are the advantages of this circuit over that of a differential amplifierrealised with a single op-amp?[6] What is the voltage gain of the whole circuit? How could the circuit

be modified to generate variable gain in the range 20 dBto 40 dB?[9] If the amplifier of Fig Q2 has a common mode rejection ratio of 120 dB, but isotherwise ideal, what is the minimum differential input voltage that should bediscernable when subjected to a 1 V common mode signal?[5]