Supplying a regulated 0.6V to biomedical systems requires a low dropout (LDO) regulator with a maximum driving current capability of 10mA. One sub-1V voltage reference circuit is commonly used in the conventional LDO design to generate the reference voltage VREF with a low temperature coefficient (TC), as shown in Fig. 17.10.1. VREF is sent to the inverting terminal of the error amplifier (EA) to regulate the output voltage VOUT. The critical path of the voltage headroom exists between V REF and VIN through the inverting terminal and the tail current of the EA. That is, VIN>VSG+V OV+VREF ≈|Vtp|+2VOV+V REF, where VIN is the input supply voltage, Vtp is the threshold voltage of the p-type MOSFET and VOV is the overdrive voltage. If the minimum value of VIN is reduced to 0.65V, the derived VREF should be smaller than 50mV when |Vtp| is 0.4V and |VOV| is 0.1V. Such a sub-1V voltage reference circuit is difficult to design -. Even if VREF can be derived, the offset voltage in the EA will seriously affect the exact value of VREF (≤50mV). In addition, the low noise immunity is another disadvantage that severely affects the performance of the biomedical system.