Compensation technique providing stability over broad range of output capacitor values
First Claim
1. A voltage regulator receiving an input voltage and operative over a specified range of output capacitances at a load comprising:
- a control circuit responsive to load voltage for generating an error signal indicative of a difference thereof from a reference voltage; and
an output stage responsive to the error signal for providing regulated voltage to the load, the output stage comprising;
(a) a metal oxide semiconductor (MOS) pass transistor having a source and a drain coupled between an input voltage source and the load and having a gate for controlling voltage drop across the MOS pass transistor to provide the regulated voltage at the load; and
(b) an input transistor circuit responsive to the error signal and coupled to control operation of the MOS pass transistor, the input transistor circuit presenting a shunt impedance to the error signal for values of output capacitances within a portion of the range of output capacitances so as to stabilize closed loop gain of the voltage regulator for output capacitances within that portion.
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Accused Products
Abstract
A disclosed amplifier and buffer circuit, for example for a linear voltage regulator, comprises an input gain stage, an integrator and a unity-gain output stage. An output stage compensation scheme enables stable operation over a broad range of output capacitance. For low to moderate output capacitance, the design of the output stage effectively pushes the output pole to high frequencies while an internal pole provided by the integrator is dominant and rolls off the gain at lower frequencies. For high output capacitance, an input impedance of the buffer couples the internal pole and output pole, such that the output pole becomes dominant while the internal pole gets pushed to higher frequencies, maintaining stability. This input impedance connection may utilize the base-emitter resistance of a bipolar junction transistor connected to the internal node, or the connection may use an MOS transistor and a separate RC circuit.
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Citations
39 Claims
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1. A voltage regulator receiving an input voltage and operative over a specified range of output capacitances at a load comprising:
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a control circuit responsive to load voltage for generating an error signal indicative of a difference thereof from a reference voltage; and an output stage responsive to the error signal for providing regulated voltage to the load, the output stage comprising; (a) a metal oxide semiconductor (MOS) pass transistor having a source and a drain coupled between an input voltage source and the load and having a gate for controlling voltage drop across the MOS pass transistor to provide the regulated voltage at the load; and (b) an input transistor circuit responsive to the error signal and coupled to control operation of the MOS pass transistor, the input transistor circuit presenting a shunt impedance to the error signal for values of output capacitances within a portion of the range of output capacitances so as to stabilize closed loop gain of the voltage regulator for output capacitances within that portion. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A voltage regulator, comprising:
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a control circuit for monitoring a voltage proportional to a load voltage and generating an error signal indicative of a difference thereof from a reference voltage; and an output stage responsive to the error signal for providing a regulated voltage to the load, the output stage comprising; (a) a metal oxide semiconductor (MOS) pass transistor having a source and a drain coupled between a source of the input voltage and the load and having a gate for controlling voltage drop across the MOS pass transistor to provide regulated voltage to the load; and (b) an input transistor comprising a bipolar junction transistor (BJT) having a base receiving the error signal and being coupled to control the MOS pass transistor. - View Dependent Claims (16, 17, 18, 19, 20, 21)
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22. A voltage regulator operative over a specified range of output capacitances comprising:
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an amplifier coupled to receive regulated load voltage; an integrator responsive to an output of the amplifier for providing an error signal, wherein the integrator is configured to stabilize closed loop gain of the voltage regulator for output capacitance values within a first portion of the specified range of output capacitances; and a unity gain output stage coupled to an input voltage source for supplying the regulated voltage to the load in response to the error signal, wherein the unity gain output stage is configured to stabilize the closed loop gain of the voltage regulator for output capacitance values in a second portion of the specified range of capacitance values higher than the first portion.
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23. A circuit coupled to an input signal source and configured for responsively producing an output signal, comprising:
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a greater than unity gain amplifier coupled to the output signal; an integrator coupled to an output of the amplifier; and an output stage buffer for processing the input signal in response to a signal from the integrator, to supply the output signal to a load, wherein; the integrator is configured to stabilize the closed loop gain of the circuit over a first portion of a specified range of load capacitances; and the output stage buffer is configured to stabilize closed loop gain of the circuit over a second portion of the specified range of capacitances higher than the first portion. - View Dependent Claims (24, 25, 26, 27, 28, 29, 30, 31)
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32. A circuit operative throughout a specified range of output capacitances, and supplying an output signal to a load, comprising:
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an amplifier for monitoring a voltage proportional to the output signal load to generate an error signal indicative of a difference thereof from a reference voltage; and a buffer, responsive to the error signal, to supply the output signal, the buffer comprising; (a) a metal oxide semiconductor (MOS) pass transistor having a source and a drain coupled between the input signal and the load and having a gate for controlling voltage drop across the MOS pass transistor; and (b) an input transistor circuit responsive to the error signal, coupled to control operation of the MOS pass transistor, the input transistor circuit presenting a shunt impedance to the error signal for values of output capacitances in a portion of the range of output capacitances so as to stabilize closed loop gain over that portion of the range. - View Dependent Claims (33, 34, 35, 36, 37, 38)
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39. A circuit for supplying an output signal to a load, comprising:
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an amplifier for monitoring a voltage proportional to the output signal, to generate an error signal indicative of a difference thereof from a reference voltage; an integrator coupled to receive the error signal and producing an integrated error signal; an output stage responsive to the integrated error signal for producing the output signal, the output stage comprising; (a) a metal oxide semiconductor (MOS) pass transistor having a source and a drain coupled between the input signal and the output and having a gate for controlling voltage drop across the MOS pass transistor to provide the output signal; and (b) a bipolar junction transistor (BJT) having a base receiving the integrated error signal, coupled to control operation of the MOS pass transistor.
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Specification