Compensation of LDO regulator using parallel signal path with fractional frequency response
First Claim
1. A low drop out (LDO) voltage regulator comprising:
- (a) a pass transistor having a first electrode coupled by an output conductor to a load and a second electrode coupled to an input voltage;
(b) an error amplifier having a first input coupled to a reference voltage, a second input connected to a feedback conductor, and an output coupled to a control electrode of the pass transistor;
(c) a parallel path transistor having a first electrode coupled to the input voltage, a control electrode coupled to the output of the error amplifier, and a second electrode coupled to the feedback conductor; and
(d) a feedback resistance coupled between the feedback conductor and the output conductor.
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Abstract
A low drop out (LDO) voltage regulator (10) includes a pass transistor (MPpass) having a source coupled by an output conductor (4) to a load and a drain coupled to an input voltage to be regulated. An error amplifier (2) has a first input coupled to a reference voltage, a second input connected to a feedback conductor (4A), and an output coupled to a gate of the pass transistor. A parallel path transistor (MPpa) has a source coupled to the input voltage, a gate coupled to the output (3) of the error amplifier (2), and a drain coupled to the feedback conductor. A feedback resistor (Rf) is coupled between the feedback conductor and the output conductor.
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Citations
20 Claims
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1. A low drop out (LDO) voltage regulator comprising:
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(a) a pass transistor having a first electrode coupled by an output conductor to a load and a second electrode coupled to an input voltage; (b) an error amplifier having a first input coupled to a reference voltage, a second input connected to a feedback conductor, and an output coupled to a control electrode of the pass transistor; (c) a parallel path transistor having a first electrode coupled to the input voltage, a control electrode coupled to the output of the error amplifier, and a second electrode coupled to the feedback conductor; and (d) a feedback resistance coupled between the feedback conductor and the output conductor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A method of operating a low drop out (LDO) voltage regulator with low quiescent current and at least a predetermined phase margin despite large variations in load current, the method comprising:
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(a) applying an input voltage to a first electrode of a pass transistor and coupling a second electrode of the pass transistor to an output conductor applying an output voltage to a load; (b) coupling a first input of an error amplifier to a reference voltage, and coupling an output of the error amplifier to a control electrode of the pass transistor; (c) coupling a feedback resistance between the output conductor and a second input of the error amplifier; and (d) compensating the LDO voltage regulator by coupling a parallel path transistor between the input voltage and the second input of the error amplifier and by coupling a control electrode of the parallel path transistor to the output of the error amplifier. - View Dependent Claims (16, 17, 18, 19)
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20. A low drop out (LDO) voltage regulator with low quiescent current and at least a predetermined phase margin despite large variations in load current, comprising:
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(a) a pass transistor and means for applying an input voltage to a first electrode of the pass transistor and means for coupling a second electrode of the pass transistor to apply an output voltage to a load; (b) means for coupling a first input of an error amplifier to a reference voltage and means for coupling an output of the error amplifier to a control electrode of the pass transistor; (c) means for coupling a feedback resistance between the output voltage and a second input of the error amplifier; and (d) parallel path means coupled between the input voltage and the second input of the error amplifier for compensating a feedback loop of the LDO voltage regulator.
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Specification