Linear step-down voltage regulator

A linear step-down voltage regulator, being grounded to a plurality of analog ground terminals, the ground terminal being electrically connected to a digital ground terminal of a switching circuit, the linear step-down voltage regulator comprising:

• a pass element, having an input terminal, an output terminal, and a control terminal, wherein the input terminal of the pass element is coupled to a power supply;
• a voltage dividing resistor, coupled between the pass element and the ground terminal, wherein an output voltage is generated at a location where the voltage dividing resistor and the pass element are coupled together, and the voltage dividing resistor provides a feedback voltage is directly proportional to the output voltage;
• an error amplifier, having a first input terminal, a second input terminal, and an output terminal, wherein the first input terminal of the error amplifier receives the feedback voltage, the second input terminal of the error amplifier receives a reference voltage;
• a metal oxide semiconductor (MOS) transistor, having a gate, a source, and a drain, wherein the gate of the MOS transistor is coupled to the output terminal of the error amplifier, the source of the MOS transistor is coupled to the ground terminal;
• and
• a low-pass filter, coupled between the drain of the MOS transistor and the control terminal of the pass element for depressing a switching noise originated from the switching circuit.