voltage regulator 2 must be inserted between the external supply voltage and the digital core 3 the voltage regulator 2 creates a voltage drop between the external supply voltage and the digital core 3 ensuring that v core u2014 max gt v reg u2014 max for proper operation of the device it is also necessary to have v in u2014 min gt v core u2014 min and v reg u2014 min gt v core u2014 min for earlier semiconductor technologies using batteries as a power source the voltage regulator was in many cases not needed since v core u2014 max gt v in u2014 max i e the supply voltage range included the battery voltage for designs using current semiconductor technologies or using other types of power generators this is in general not the case and a voltage regulator is required this problem also arises in the field of energy harvesting devices as these frequently generate relatively high voltages in order to operate correctly the voltage regulator draws a certain amount of current in its control circuits this current called the regulator bias current is drawn from the battery in addition to the current required by the digital core several design techniques are available to obtain sufficient circuit performance with very low current consumption nevertheless the voltage regulator bias current is of the same order of magnitude as the supply current to the digital core when in sleep mode thus the regulator increases the load on the power source which in turn means that the power source must be increased leading to added size weight and.