17.10 0.65V-input-voltage 0.6V-output-voltage 30ppm/°C low-dropout regulator with embedded voltage reference for low-power biomedical systems

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 V_REF with a low temperature coefficient (TC), as shown in Fig. 17.10.1. V_REF is sent to the inverting terminal of the error amplifier (EA) to regulate the output voltage V_OUT. The critical path of the voltage headroom exists between V_REF and V_IN through the inverting terminal and the tail current of the EA. That is, V_IN>V_SG+V_OV+V_REF ≈|V_tp|+2V_OV+V_REF, where V_IN is the input supply voltage, V_tp is the threshold voltage of the p-type MOSFET and V_OV is the overdrive voltage. If the minimum value of V_IN is reduced to 0.65V, the derived V_REF should be smaller than 50mV when |V_tp| is 0.4V and |V_OV| is 0.1V. Such a sub-1V voltage reference circuit is difficult to design [1]-[4]. Even if V_REF can be derived, the offset voltage in the EA will seriously affect the exact value of V_REF (≤50mV). In addition, the low noise immunity is another disadvantage that severely affects the performance of the biomedical system.