The four types of the Z-state circuits basically include a sensing gate, two stacked PMOS transistors, and a feedback line. The sensing gate senses a voltage at its input assuming no feedback is applied. Again, the corresponding output of two stacked PMOS transistors is assumed to be connected to the sensing input. Two stacked PMOS transistors generate a high impedance Z-state at its output according to the corresponding gate voltages. Therefore, the feedback line keeps sampling the output and feeding back the output voltage to the sensing input. Consequently, the feedback configuration provides the initial output voltage, which is the midpoint voltage decided by the device aspect ratios of the sensing gate before normal operation starts.