Controlling the drop-out voltage of the regulators
There are some specific devices available which can do drop-out control. These devices are called power filters. Power filters are similar to low-dropout regulators except that instead of regulating output voltage relative to ground, a power filter regulates output voltage relative to input voltage. In other words, a power filter maintains a fixed drop-out or delta-V from input to output. Since power filters can control the delta-V, they can be optimized for high power supply rejection ratio or PSRR with a lower vin-to-vout delta. This helps in lower power dissipation than standard regulators and LDOs. The power filters have very good noise performance because the bandgap and noise associated with the device are never gained up resulting in low output noise regardless of output voltage.