Claims
- 1. A low voltage dropout circuit comprising:
- a dropout circuit input and a dropout circuit output and a low voltage port;
- a path element coupled between the dropout circuit input and the dropout circuit output, the path element having a control port and a parasitic capacitance;
- a first capacitor having a first and a second port, the first port of the capacitor coupled to the dropout circuit input;
- an amplifier having a first and a second input and an output, the first input of the amplifier coupled to the reference voltage, the second input of the amplifier coupled to the dropout circuit output, the output of the amplifier coupled to the second port of the first capacitor;
- a voltage buffer having a first port and a second port, the first port of the voltage buffer coupled to the output of the amplifier and the second port of the voltage buffer coupled to the control port of the path element;
- a second capacitor having a first and a second port, the first port of the second capacitor coupled to the dropout circuit output;
- a current buffer having a first port and a second port, the second port of the current buffer coupled to the output of the amplifier and the first port of the current buffer coupled to the second port of the second capacitor.
- 2. A dropout circuit as recited in claim 1, further comprising:
- a voltage divider coupled between the dropout circuit output and the low voltage port;
- a node within the voltage divider coupled between the second input of the amplifier and the dropout circuit output.
- 3. A dropout circuit as recited in claim 1, wherein the path element has a Miller effect and the current buffer reduces the Miller effect with respect to the second capacitor.
- 4. A dropout circuit as recited in claim 1, wherein the current buffer comprises a virtual AC ground coupled to the second terminal of the second capacitor.
- 5. A dropout circuit as recited in claim 1, wherein the voltage buffer is a voltage buffer amplifier.
- 6. A dropout circuit as recited in claim 1, wherein the amplifier is a transconductance amplifier.
- 7. A dropout circuit as recited in claim 1, wherein the path element is a PMOSFET transistor having a gate, and wherein the control port of the path element comprises the gate.
- 8. A dropout circuit as recited in claim 1, wherein, the amplifier is a differential amplifier.
- 9. A method for generating a regulated voltage source at an output port from an unregulated voltage at an input port, the method comprising:
- controlling the flow of a first current between the input and the output ports with at least one path component having a parasitic capacitance;
- generating a feedback voltage based upon the voltage at the output port;
- comparing the feedback voltage with a predetermined voltage;
- providing a second current based upon the comparison of the feedback voltage with the predetermined voltage;
- generating a third current by capacitive coupling to the output port and current buffering the capacitive current;
- summing the second and the third currents at a node;
- coupling a capacitor between the input port and the node;
- voltage buffering a sum of currents at the node to provide the control of the flow of the current through the path component.
- 10. The method of claim 9, wherein the step of generating a feedback voltage based upon the voltage at the output port comprises the steps of
- coupling a voltage divider between the output port and a low voltage port;
- coupling the feedback voltage from a node within the voltage divider.
- 11. A method for making a low voltage dropout integrated circuit, the method comprising:
- forming in the integrated circuit a path element having a control electrode between an input port and an output port;
- forming a feedback voltage circuit in the integrated circuit having a node;
- coupling the node to the output port;
- forming a reference voltage generator in the integrated circuit;
- forming an amplifier in the integrated circuit for determining the difference between the voltage at the node and the reference voltage generator;
- forming a voltage buffer coupled between an output of the amplifier and the control electrode of the path element such that flow of current through the path element results in the voltage at the output port being about a predetermined multiple of the reference voltage;
- forming a compensating capacitance path between the output port and the output of the amplifier such that a compensating capacitance is isolated to thereby avoid any feed forward circuit path;
- forming a second compensating capacitance path between the input port and the output of the amplifier.
- 12. A method for making an integrated circuit power supply, the method including:
- forming input and output ports and a path element having a control electrode coupling the input to the output port;
- forming an amplifier responsive to a voltage difference between a reference voltage and a voltage proportional to the voltage at the output port;
- forming a voltage buffer between an output of the amplifier and the control electrode of the path element such that the control electrode of the path element is responsive to the output of the amplifier;
- forming a virtual AC ground in the circuit; and
- forming a first compensating capacitance coupling the virtual AC ground to the output port, whereby frequency stability of the circuit is improved;
- forming a second compensating capacitance coupled between the input port and the output of the amplifier.
- 13. The method of claim 12, wherein the step of forming a virtual AC ground comprises forming a current buffer and coupling the current buffer to the output of the amplifier.
Parent Case Info
This application is a continuation-in-part of a application, Ser. No. 08/376,028, filed on Jan. 20, 1995, now U.S. Pat. No. 5,552,697, and assigned to Linfinity Microelectronics Inc.
US Referenced Citations (4)
Continuation in Parts (1)
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Number |
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376028 |
Jan 1995 |
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