LDO with improved stability

A modified low drop-out voltage regulator, comprising:

• an amplifier to amplify input signals, having as inputs an input node and a reference node, and an output node;
• a buffer followed by a pmos transistor, said buffer having a buffer input node coupled to said amplifier output node and further having an output node;
• a pass device of a current mirror, said pass device having an input node coupled to said buffer output node and having an output node, said pass device further comprising:
• a first pmos transistor representing a first output side of said current mirror, the drain of said first pmos transistor coupled to said pass device output node;
• a second pmos transistor representing a second output side of said current mirror, the drain of said second pmos transistor, in series with a resistor, paralleled to said first pmos transistor, the junction of said drain of said second pmos transistor and said resistor providing a feedback node;
• a bond wire coupled at one end to said pass device output node and coupled at its other end to a low drop-out voltage regulator output node;
• said resistor, in series with said bond wire, coupled to said low drop-out voltage regulator output node;
• a main feedback loop to regulate an output voltage Vout at said low drop-out voltage regulator output node, where one end is coupled to the junction of said bond wire and said low drop-out voltage regulator output node and the other end is coupled to said amplifier input node;
• and
• a fast feedback loop to feed back high-frequency disturbances from said low drop-out voltage regulator output node, said fast feedback loop comprising a Miller feedback capacitor where one end of said fast feedback loop is coupled to said feedback node and where the other end is coupled to said buffer input node.

A method of moving a high-frequency zero back into the bandwidth of a low drop-out voltage regulator, comprising the steps of:

• a) providing a feedback input to an amplifier;
• b) coupling a buffer to the output of said amplifier;
• c) coupling a first pass device between the output of said buffer and a wire bond;
• d) paralleling a second pass device, in series with a resistor, with said first pass device thereby creating an extra equivalent series resistance to move a zero of said low drop-out voltage regulator within its bandwidth;
• e) coupling the second pass device in series with said resistor and said wire bond to the output of said low drop-out voltage regulator;
• f) creating a main feedback loop from the junction of said bond wire and said output of said low drop-out voltage regulator to said feedback input of said amplifier;
• and
• g) creating a fast feedback loop from a junction of said second pass device in series with said resistor to an input of said buffer via a Miller capacitor.