Adaptable low dropout (ldo) voltage regulator and method therefor

An adaptable LDO regulator for use with a low-noise voltage controlled oscillator or the like, the adaptable LDO regulator comprising:

• an error amplifier having a non-inverting input for receiving a reference voltage, an inverting input for receiving a feedback voltage from a feedback terminal, and an output;
• a lowpass filter having an input coupled to said output of said error amplifier, and an output;
• a first pass transistor having a first current electrode for receiving an input voltage, a control electrode coupled to said output of said lowpass filter, and a second current electrode;
• a voltage divider having a first terminal, and a second terminal coupled to a voltage reference terminal, and an intermediate terminal for providing said feedback voltage;
• and
• a second pass transistor having a first current electrode for receiving said input voltage, a control electrode coupled to said output of said lowpass filter, and a second current electrode for providing an output voltage;
• and
• a mode selection network that:
• in a closed loop mode, couples said second current electrode of said first pass transistor to said second current electrode of said second pass transistor and to said input of said voltage divider, and
• in an open loop mode, couples said second current electrode of said first pass transistor to said input of said voltage divider and decouples said second current electrode of said second pass transistor from said second current electrode of said first pass transistor and said first terminal of said voltage divider.

A method comprising:

• providing an error voltage in response to a difference between a feedback voltage and a reference voltage;
• controlling a conductivity of a first pass transistor in response to said error voltage, said first pass transistor having a first current electrode for receiving an input voltage and a second current electrode;
• controlling a conductivity of a second pass transistor in response to said error voltage, said second pass transistor having a first current electrode for receiving said input voltage and a second current electrode providing an output voltage;
• in a closed loop mode:
• coupling said second current electrodes of said first pass transistor and said second pass transistor together;
• and
• dividing said output voltage and providing said feedback voltage in response thereto, and
• in an open loop mode:
• decoupling said second current electrode of said first pass transistor from said second current electrode of said second pass transistor;
• and
• dividing a voltage on said second current electrode of said first pass transistor, and providing said feedback voltage in response thereto.