US 5,672,959 A · Low drop-out voltage regulator having high ripple rejection and low power consumption

Abstract

A low drop-out regulator circuit that has high ripple rejection and low power consumption. A first local feedback loop is a high-speed, high-bandwidth loop that actively rejects noise from the input source to the regulator. A second feedback loop, having lower speed and a correspondingly lower bandwidth than the first feedback loop, regulates the output voltage. Each feedback loop is separately optimized for its respective bandwidth requirements and, therefore, the regulator is highly efficient. The first feedback loop comprises an amplifier and a pair of PMOS transistors configured as a current mirror with current gain. The first feedback loop generates a first current for charging an output capacitor. Feedback ensures that the first current is proportional to a second current generated by the second feedback loop while rejecting noise from the input source. The second feedback loop comprises a transconductance amplifier that controls the second current with feedback such that the first current charges the output capacitor to the desired output voltage level. The second loop has a lower bandwidth than the first loop because the bandwidth of the second feedback loop is dominated by a relatively large output capacitance and compensation capacitance, while the bandwidth of the first feedback loop is dominated by the relatively small gate capacitances of the pair of transistors and a relatively small compensation capacitance.

Claims24

Dependent claims

A voltage regulator comprising:

a. a first feedback loop for attenuating noise from a power source having a first bandwidth;
and
b. a second feedback loop including a capacitor and having a second bandwidth is coupled to the first feedback loop for generating an output voltage across the capacitor wherein the second bandwidth is limited by a capacitance of the capacitor and the first bandwidth is independent of the capacitance.

A voltage regulator comprising:

a. a first transistor having a first source, a first drain and a first gate;
b. a second transistor having a second source, a second drain and a second gate, wherein the first source is coupled to the second source;
c. an amplifier having a first amplifier input, a second amplifier input and an amplifier output, wherein the first drain is coupled to the first amplifier input, the second drain is coupled to the second amplifier input and the amplifier output is coupled to the first gate and to the second gate;
d. a first resistor having a first terminal and a second terminal wherein the first terminal of the first resistor is coupled to the second drain;
e. a transconductance amplifier having a first transconductance input, a second transconductance input and a transconductance output wherein the first transconductance input is coupled to the second terminal of the first resistor, the second transconductance input is coupled to receive a reference voltage level and the transconductance output is coupled to the first drain;
f. a second resistor having a first terminal and a second terminal wherein the first terminal of the second resistor is coupled to the second terminal of the first resistor and the second terminal of the second resistor is coupled to a ground node;
and
g. a capacitor having a first terminal and a second terminal wherein the first terminal of the capacitor is coupled to the second drain and the second terminal of the capacitor is coupled to the ground node.

5 more elements

Dependencies are inferred from the claim text.

Low drop-out voltage regulator having high ripple rejection and low power consumption

Life of this patent

Low drop-out voltage regulator having high ripple rejection and low power consumption

Life of this patent

Abstract

Claims24