Low dropout regulator, method for improving stability of low dropout regulator, and phase-locked loop

A phase-locked loop, comprising:

• a low dropout regulator, wherein the low dropout regulator comprises:
• a reference voltage source, configured to provide a reference voltage;
• an error amplifier, coupled to the reference voltage source, and configured to receive a feedback voltage and the reference voltage, compare the feedback voltage with the reference voltage, and output a control voltage according to a result of comparing the feedback voltage with the reference voltage;
• a regulating circuit, coupled to the error amplifier, and configured to receive the control voltage, and output a regulating current under control of the control voltage;
• a load, coupled to the regulating circuit and the error amplifier, wherein an on-load voltage is formed when the regulating current passes through the load, and the feedback voltage is related to the on-load voltage;
• a first compensation circuit, coupled to the regulating circuit, and configured to regulate a dominant pole and a secondary dominant pole of the low dropout regulator, so as to regulate a phase margin;
• and
• a second compensation circuit, coupled to the first compensation circuit, and configured to:
• decrease the dominant pole of the low dropout regulator and further increase the secondary dominant pole on the basis that the first compensation circuit has regulated the dominant pole and the secondary dominant pole of the low dropout regulator, so as to regulate the phase margin;
• and regulate a gain-bandwidth product of the low dropout regulator, wherein:
• the second compensation circuit comprises a compensation resistor, wherein a terminal of the compensation resistor is connected to an output terminal of the error amplifier, and another terminal of the compensation resistor is connected to a terminal of a nulling resistor and a gate of the transistor.

A method for improving stability of a low dropout regulator, comprising:

• receiving a reference voltage and a feedback voltage;
• comparing the feedback voltage with the reference voltage, and generating a control voltage according to a result of comparing the feedback voltage with the reference voltage;
• generating a regulating current under control of the control voltage;
• regulating the dominant pole and the secondary dominant pole of the low dropout regulator according to the regulating current on the basis that the dominant pole and the secondary dominant pole of the low dropout regulator are regulated according to the regulating current, and regulating a gain-bandwidth product of the low dropout regulator according to the regulating current;
• decreasing, by a compensation circuit comprising a compensation resistor, the dominant pole of the low dropout regulator and further increasing the secondary dominant pole, so as to regulate the phase margin;
• and regulate a gain-bandwidth product of the low dropout regulator, wherein a terminal of the compensation resistor is connected to an output terminal of an error amplifier, and another terminal of the compensation resistor is connected to a terminal of a nulling resistor and a gate of a transistor;
• and
• reducing noise introduced into the low dropout regulator.