The cascode transistor can be thought of as providing a "shield" for the input transistor from the voltage variations at the output. To quantify this "shielding" property of the cascode, consider the situation in Fig. P8.69. Here we have grounded the input terminal (i.e., reduced vi to zero), applied a small change vx to the output node, and denoted the voltage change that results at the drain of Q1:
by vy. By what factor is vy smaller than vx?
