Figure 8.31 illustrates the simplest, most basic approach for differential-to-single-ended
conversion. It consists of simply ignoring the drain current signal of Q1 and eliminating its
drain resistor altogether, and taking the output between the drain of Q2 and ground. The
obvious drawback of this scheme is that we lose a factor of 2 (or 6 dB) in gain as a result of
“wasting” the drain signal current of Q1. A much better approach would be to find a way of
utilizing the drain-current signal of Q1, and that is exactly what the circuit we are about to
discuss accomplishes.