The Design of High Impedance S/H Switch in Power-off State

Some times, the input-port of a single supply A/D converter needs a high impedance S/H switch when it does not supply power. Now we introduce a digital logical circuit to realize it. Through this digital logical circuit, when analog input signal is more than 0V, the analog input port to power or ground will be on high impedance state. At the same time, the analog input port also will be on high impedance state to another analog input port in power-off state.