The low-input-resistance problem of the difference amplifier of Fig. 2.16 can be solved by using
voltage followers to buffer the two input terminals; that is, a voltage follower of the type in Fig. 2.14
is connected between each input terminal and the corresponding input terminal of the difference
amplifier. However, if we are going to use two additional op amps, we should ask the question: Can
we get more from them than just impedance buffering? An obvious answer would be that we
should try to get some voltage gain. It is especially interesting that we can achieve this without compromising
the high input resistance simply by using followers with gain rather than unity-gain followers.
Achieving some or indeed the bulk of the required gain in this new first stage of the