The Horizontal Cascode
   Now for something slightly different. Rather than split the power supply, we third it into equal power supply voltages. In other words, if the single power supply had a rail voltage of 300 volts, it would be replaced with three 100 volt power supplies. (Other ratios are certainly permissible, but this ratio nicely suits the design example.) The shifted voltage relations are more complex this time. (If this circuit is immediately apprehensible to you, then I want to write an article for this journal.) For the rest of us here is the step-by-step analysis.

   The defining characteristic of the any cascode circuit is the locking of the bottom tube's cathode-to-plate voltage. The bottom triode's plate looks into the top triode's cathode, which barely moves because of the steady reference voltage fed to the its grid. This vise grip on the bottom tube works to preserve its transconductance, which is diminished in a ground cathode amplifier by the presence of the plate resistor. And it is the tube's transconductance driving the current fluctuations through the plate resistor that ultimately yields the gain of the circuit.