Methods and apparatus to reject current ripple

A low dropout regulator circuit comprising:

• an error amplifier having a first input, a second input, and an output, the first input coupled to a reference voltage, the second input coupled to an output of the low dropout regulator;
• a buffer having an input and an output, the input of the buffer coupled to the output of the error amplifier;
• a pass transistor having a control terminal, a first current terminal, and a second current terminal, the control terminal coupled to the output of the buffer, the second current terminal coupled to the output of the low dropout regulator;
• and
• a feed forward current ripple rejection circuit having an input and an output, the input of the feed forward current ripple rejection circuit coupled to the first current terminal of the pass transistor, the output of the feed forward current ripple rejection circuit coupled to the output of the low dropout regulator.

A low dropout regulator circuit comprising:

• an error amplifier configured to generate an error signal of a comparison of an output voltage to a reference voltage;
• a buffer configured to stabilize the output voltage;
• a pass transistor configured to control a flow of current through the pass transistor;
• and
• a feed forward current ripple rejection circuit in parallel with the pass transistor, the feed forward current ripple rejection circuit including:
• a sensing transistor configured to sense the current passing through the pass transistor;
• an amplifier having a gain, the amplifier configured to amplify a signal for further processing, the signal indicative of current ripple through the pass transistor;
• a feedback transistor configured to form a feedback loop with a canceling amplifier, wherein a first current terminal of the feedback transistor has a voltage equal to the reference voltage;
• and
• a canceling transistor configured to inject the signal indicative of current ripple into an output of the low dropout regulator circuit, the signal indicative of current ripple 180 degrees out of phase with a sensed current ripple.