Switch-less adaptive feed-forward supply noise cancellation technique for capacitor-less LDR

An adaptive feed-forward power supply noise cancellation technique for low-dropout regulator (LDR) which requires no switches is proposed in this paper. By utilizing replica, transconductances (g_m, g_ds) of the large pass transistor are linearly reproduced to construct a load-current-depedent ratioed feed-forward path from supply to gate of pass transistor. The power supply rejection (PSR) capability is enhanced by adaptively feeding compensation charging current to gate parasitic capacitor of the pass transistor, which is effective in a wide load range. The idea of the PSR enhancement technique is implemented in an output capacitor-less LDR in a standard 65-nm CMOS process. The total on-chip capacitance for compensation and low-pass filtering is 40pF. The output is 1.0V and delivers a maximum current of 50mA at 200mV drop-out. Simulations verify that the PSR is further enhanced in mid-frequency range (~100kHz-10MHz) compared with conventional techniques, without feed-forward ratio selection via switches, and it generates ignorable effects on stability and 200-ns full load transient response.