Low dropout regulator with stability compensation circuit
First Claim
1. A stability compensation circuit for a low dropout regulator, the low dropout regulator including a driver transistor, the circuit comprising:
- a first compensation transistor having a gate coupled to a gate of the driver transistor, a source coupled to an unregulated input voltage, and a drain;
a compensation capacitor coupled between the gate and the drain of the compensation transistor;
a second compensation transistor having a gate coupled to a drain of the driver transistor, a drain coupled to the unregulated input voltage, and a source;
a resistor coupled between the drain of the first compensation transistor and the source of the second compensation transistor; and
a source of bias current coupled to the source of the second compensation transistor,wherein the compensation capacitor remains in an accumulation region at no load current to provide a maximum capacitance, and the capacitance of said compensation capacitor decreases with a load current during a higher load current region.
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Accused Products
Abstract
The present invention provides a low dropout (LDO) regulator with a stability compensation circuit. A “zero frequency” tracking as well as “non-dominant parasitic poles'"'"' frequency reshaping” are performed to achieve a good phase margin for the LDO by means of the compensation circuit. In this compensation method neither a large load capacitor nor its equivalent series resistance is needed to stabilize a regulator. LDO regulators, in system on chip application, having load capacitors in the range of few nano-Farads to few hundreds of nano-Farads can be efficiently compensated with this compensation method. A dominant pole for the regulator is realized at an internal node and the second pole at an output node of the regulator is tracked with a variable capacitor generated zero over a range of load current to cancel the effect of each other. A third pole of the system is pushed out above the unity gain frequency of the open loop transfer function with the help of the frequency compensation circuit. The compensation technique is very effective in realizing a low power, low-load-capacitor LDO desirable for system on chip applications.
31 Citations
20 Claims
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1. A stability compensation circuit for a low dropout regulator, the low dropout regulator including a driver transistor, the circuit comprising:
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a first compensation transistor having a gate coupled to a gate of the driver transistor, a source coupled to an unregulated input voltage, and a drain; a compensation capacitor coupled between the gate and the drain of the compensation transistor; a second compensation transistor having a gate coupled to a drain of the driver transistor, a drain coupled to the unregulated input voltage, and a source; a resistor coupled between the drain of the first compensation transistor and the source of the second compensation transistor; and a source of bias current coupled to the source of the second compensation transistor, wherein the compensation capacitor remains in an accumulation region at no load current to provide a maximum capacitance, and the capacitance of said compensation capacitor decreases with a load current during a higher load current region. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. A stability compensation circuit for a low dropout regulator, the low dropout regulator including a driver transistor, the circuit comprising:
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a first compensation transistor having a gate coupled to a gate of the driver transistor, a source coupled to an unregulated input voltage, and a drain; a compensation capacitor coupled between the gate and the drain of the compensation transistor; a second compensation transistor having a gate coupled to a drain of the driver transistor, a drain coupled to the unregulated input voltage, and a source; a resistor coupled between the drain of the first compensation transistor and the source of the second compensation transistor; a source of bias current coupled to the source of the second compensation transistor; a first pole for the regulator realized at an internal node; and a second pole at an output node of the regulator that is tracked with a variable compensation capacitor generated zero over a range of load current. - View Dependent Claims (20)
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Specification