MOSFET Active Battery (Floating Active Level Shifter)

The circuit buffers the input current and maintains a voltage difference (Vbatt) between the source (input current) and the load. The voltage difference is the sum of the gate to source voltages of the two MOSFETs (Vgs1 + Vgs2). The voltage difference can be made approximately constant by keeping Vgs1 large relative to Vgs2. This can be done by keeping the bias current large relative to the input current. The saved values has small bias current relative to input current. With body effect ignored Id = ½ · µn · Cox (W/L) (Vgs - VTO)² In Multisim KP = µn · Cox Id = ½ · KP (W/L) (Vgs - VTO)² W is left equal to L and the factor (W/L) is dropped Id = ½ · KP (Vgs - VTO)² Vgs = (√(2Id/KP)) + VTO VTO (Threshold voltage) set to 1 V for both MOSFETs. Vgs2 = (√(2·Id2/KP2)) + VTO2 Vgs2 = (√(2·100 µA / (20 µA/V²))) + 1 V Vgs2 = (√(10 V²)) + 1 V Vgs2 = 3.1622776601683793319988935444327 V + 1 V Vgs2 = 4.1622776601683793319988935444327 V To shift by 6 V Vgs1 = Vbatt - Vgs2 Vgs1 = 6 V - 4.1622776601683793319988935444327 V Vgs1 = 1.8377223398316206680011064555673 V Id1 = ½ · KP1 (Vgs1 - VTO1)² Id1 = ½ · 20 µA/V² (1.8377223398316206680011064555673 V - 1 V)² Id1 = 10 µA/V² (0.83772233983162066800110645556728 V)² Id1 = 7.0177871865296534400885164453825 µA