Voltage regulator with improved power supply rejection ratio characteristics and narrow response band

A voltage regulator comprising:

• first and second power supply terminals;
• an output terminal;
• a reference voltage generating circuit adapted to generate a reference voltage;
• a drive transistor connected between said first power supply terminal and said output terminal, said drive transistor having a control terminal;
• a voltage divider connected between said output terminal and said second power supply terminal, said voltage divider adapted to generate a feedback voltage between voltages at said output terminal and said first power supply terminal;
• a differential amplifier having a first input connected to said voltage divider, a second input connected to said reference voltage generating circuit and an output connected to the control terminal of said drive transistor, said differential amplifier adapted to generate an error voltage in accordance with said feedback voltage and said reference voltage and transmit said error voltage to the control terminal of said drive transistor;
• an oscillation preventing capacitor connected between the control terminal of said drive transistor and said output terminal;
• a plurality of capacitors associated with switches, connected between said first power supply terminal and the first input of said differential amplifier;
• and
• a control circuit connected to said plurality of capacitors and adapted to select said plurality of capacitors in accordance with a resistance of an external load connected to said output terminal.

A voltage regulator comprising:

• first and second power supply terminals;
• an output terminal;
• a reference voltage generating circuit adapted to generate a reference voltage;
• a drive transistor connected between said first power supply terminal and said output terminal and outputting an output voltage to said output terminal, said drive transistor having a control terminal;
• a feedback circuit receiving said output voltage and generating a feedback voltage according to said output voltage;
• a control circuit receiving said reference voltage at a reference terminal thereof and said feedback voltage at a feedback terminal thereof, said control circuit generating a control voltage by comparing said feedback voltage with said reference voltage and outputting said control voltage to said control terminal of said drive transistor;
• and
• a first capacitor connected between said first power supply and said feedback terminal.