Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2000-01-11
2001-05-01
Berhane, Adolf Deneke (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
C323S284000
Reexamination Certificate
active
06225795
ABSTRACT:
BACKGROUND
The present invention relates generally to voltage regulators, and more particularly to control systems for switching voltage regulators.
Voltage regulators, such as DC to DC converters, are used to provide stable voltage sources for electronic systems. Efficient DC to DC converters are particularly needed for battery management in low power devices, such as laptop notebooks and cellular phones. Switching voltage regulators (or simply “switching regulators”) are known to be an efficient type of DC to DC converter. A switching regulator generates an output voltage by converting an input DC voltage into a high frequency voltage, and filtering the high frequency input voltage to generate the output DC voltage. Specifically, the switching regulator includes a switch for alternately coupling and decoupling an unregulated input DC voltage source, such as a battery, to a load, such as an integrated circuit. An output filter, typically including an inductor and a capacitor, is coupled between the input voltage source and the load to filter the output of the switch and thus provide the output DC voltage. The switch is typically controlled by a pulse modulator, such as a pulse width modulator or a pulse frequency modulator, which controls the switch. A feedback circuit generates a control signal which controls the duty cycle of the pulse modulator in order to maintain the output voltage at a substantially uniform level.
In traditional switching regulators, the feedback controller continuously measures the output voltage and uses this measurement to continuously generate a control signal for the pulse modulator. Such a continuous feedback controller operates using analog circuits, such as resistors, capacitors and op-amps. Unfortunately, these analog circuits are expensive and/or difficult to fabricate as integrated circuits. Specifically, special techniques are needed to fabricate resistors in semiconductor devices. In addition, these analog circuits do not easily interface with any digital circuits that may be fabricated in the same semiconductor device.
SUMMARY
In one aspect, the invention is directed to a voltage regulator having an input terminal to be coupled to an input voltage source and an output terminal to be coupled to a load. The voltage regulator includes a power switch to alternately couple and decouple the input terminal to the output terminal with a variable duty cycle, a filter disposed between the input terminal and the output terminal to provide a substantially DC voltage at the output terminal, a sampling circuit to make measurements of an electrical characteristic of the voltage regulator at discrete moments of time, and a feedback circuit coupled to the sampling circuit and the power switch, the feedback circuit configured to use the measurements to control the duty cycle to maintain the DC voltage substantially constant.
Implementations of the invention may include the following. The electrical characteristic may be a voltage at the output terminal or a current passing through the filter. The sampling circuit may include a capacitor, a first sampling switch connecting the capacitor to the output terminal, and a second sampling switch connecting the capacitor to the feedback circuit, so that the measurement is made when the first sampling switch opens, is stored as a charge in the capacitor, and is provided to the feedback circuit when the second sampling switch closes. Alternately, the sampling circuit may include a capacitor, a first sampling switch connecting a first plate of the capacitor to a first terminal of the power switch, a second sampling switch connecting a second plate of the capacitor to a second terminal of the power switch, and a third sampling switch connecting the capacitor to the feedback circuit, so that the measurement is made when the first and second sampling switches open, is stored as a charge in the capacitor, and is provided to the feedback circuit when the third sampling switch closes. The sampling circuit may make the measurement just prior to the power switch opening and/or closing. The sampling circuit may make a first measurement of the electrical characteristic when the power switch is closed and make a second measurement of the electrical characteristic when the power switch is open. The feedback circuit may use an average of the first and second measurements to control the duty cycle. The sampling circuitry may include a capacitor, a first sampling switch connecting the capacitor to an electrical path between the input terminal and the output terminal, and a second sampling switch connecting the capacitor to the feedback circuit. The second sampling switch may be configured to close when the first sampling switch open, and the first sampling switch may be configured to open just before the power switch opens and/or closes. The power switch may be driven by a switching voltage waveform and the sampling switches may be driven by a sampling voltage waveform, and the voltage regulator may further include a timing circuit to delay the switching voltage waveform relative to the sampling voltage waveform, e.g., by approximately the time constant delay of the sampling circuit. The feedback circuit may generate a control signal, and the voltage regulator may further include a pulse modulator connected to the feedback circuit and the power switch to set the duty cycle in response to the control signal. The feedback circuit may include one or more switched-capacitor circuits coupled to the sampling circuit to convert the measurement into a charge and to generate the control signal from the charge. The sampling circuit may include an analog-to-digital converter (ADC) coupled to the sampling circuit to convert the measurement into a digital signal, and a processor coupled to the ADC to generate the control signal from the digital signal. The power switch may include a first switch connecting the input terminal to an intermediate terminal and a rectifier, such as a second switch, connecting the intermediate terminal to ground, and the output filter may be connected between the intermediate terminal and the output terminal.
In another aspect, the invention is directed to a voltage regulator having an input terminal to be coupled to an input voltage source and an output terminal to be coupled to a load. The voltage regulator includes a power switch to alternately couple and decouple the input terminal to the output terminal with a variable duty cycle, a filter disposed between the switch and the output terminal to provide a substantially DC voltage at the output terminal, a sampling circuit to make a measurement of a current passing through the output filter, and a feedback circuit connected to the sampling terminal and the power switch configured to use the measurement to control the duty cycle to maintain the DC voltage at a substantially constant level. The sampling circuit includes a capacitor, a first sampling switch connecting a first plate of the capacitor to a first terminal of the power switch, a second sampling switch connecting a second plate of the capacitor to a second terminal of the power switch, and a third sampling switch connecting the capacitor to a sampling terminal.
Advantages of the invention may include the following. The feedback controller of the voltage regulator uses a discrete-time data sampling system to control the pulse modulator. Such a feedback controller may be implemented using digital and/or switched-capacitor based circuitry, and may be fabricated using known processes suitable for complimentary metal oxide semiconductor (CMOS) fabrication techniques. This reduces the number of discrete (off-chip) components in the controller. The invention permits the feedback controller to be implemented using an analog-to-digital converter and a micro-processor so that the duty cycle of the switch may be controlled by a software-implemented algorithm. In addition, the use of digital designs and traditional CMOS fabrication techniques permit the voltage regulator to be constructed more cheaply. Furthermore, the
Clark William A.
Lidsky David B.
Stratakos Anthony J.
Berhane Adolf Deneke
Fish & Richardson P.C.
Volterra Semiconductor Corporation
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