Drive circuit for reactive loads
First Claim
Patent Images
1. A circuit for driving a reactive load with high efficiency, the circuit comprising:
- a driver circuit for converting DC input current to RF output current, the driver circuit including only one switch, the driver circuit further including a switch capacitor and a switch inductor, the switch having a nonlinear output capacitance, the switch capacitor being equal to a maximum of the switch output capacitance to minimize the effects of the nonlinear output capacitance of the switch, wherein the switch capacitor has a value of (1/(2π
FsXcs)), wherein Xcs≦
Rs/2, Fs being the resonance frequency of the switch, Xcs being the impedance of the switch capacitor, and Rs being the series output resistance of the driver circuits;
an output resonant circuit including the reactive load; and
a coupling reactance coupled in series between the RF output current of the driver circuit and an input of the output resonant circuit, the coupling reactance performing a series to parallel impedance match from the driver circuit to the output resonant circuit.
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Abstract
A highly efficient resonant switching driver circuit includes a matching reactance coupled between an output resonant circuit and a driver circuit. The matching reactance performs a series to parallel impedance match from the driver circuit to the output resonant circuit.
63 Citations
6 Claims
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1. A circuit for driving a reactive load with high efficiency, the circuit comprising:
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a driver circuit for converting DC input current to RF output current, the driver circuit including only one switch, the driver circuit further including a switch capacitor and a switch inductor, the switch having a nonlinear output capacitance, the switch capacitor being equal to a maximum of the switch output capacitance to minimize the effects of the nonlinear output capacitance of the switch, wherein the switch capacitor has a value of (1/(2π
FsXcs)), wherein Xcs≦
Rs/2, Fs being the resonance frequency of the switch, Xcs being the impedance of the switch capacitor, and Rs being the series output resistance of the driver circuits;an output resonant circuit including the reactive load; and a coupling reactance coupled in series between the RF output current of the driver circuit and an input of the output resonant circuit, the coupling reactance performing a series to parallel impedance match from the driver circuit to the output resonant circuit.
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2. A circuit for driving a reactive load with high efficiency, the circuit comprising:
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a driver circuit for converting DC input current to RF output current, the driver circuit including only one switch, the driver circuit further including a switch capacitor and a switch inductor, the switch having a nonlinear output capacitance, the switch capacitor being equal to a maximum of the switch output capacitance to minimize the effects of the nonlinear output capacitance of the switch, wherein the switch inductor is selected to have a value of (1/(4π
2 Fs2 Cs)), wherein Fo<
Fs<
2Fo, Fs being the switch resonance frequency, Cs being the value of the switch capacitor, and Fo being the operating frequency of the circuit;an output resonant circuit including the reactive load; and a coupling reactance coupled in series between the RF output current of the driver circuit and an input of the output resonant circuit, the coupling reactance performing a series to parallel impedance match from the driver circuit to the output resonant circuit.
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3. A circuit for driving a reactive load with high efficiency, the circuit comprising:
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a driver circuit for converting DC input current to RF output current, the driver circuit including only one switch, the driver circuit further including a switch capacitor and a switch inductor, the switch having a nonlinear output capacitance, the switch capacitor being equal to a maximum of the switch output capacitance to minimize the effects of the nonlinear output capacitance of the switch, wherein the values of the switch, switch inductor and switch capacitor are selected so that the Q of the switch resonance is less than one when the switch is closed and greater than or equal to two when the switch is open; an output resonant circuit including the reactive load; and a coupling reactance coupled in series between the RF output current of the driver circuit and an input of the output resonant circuit, the coupling reactance performing a series to parallel impedance match from the driver circuit to the output resonant circuit.
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4. A circuit for driving a reactive load with high efficiency, the circuit comprising:
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a driver circuit for converting DC input current to RF output current, the driver circuit having a differential implementation including a first switch and a second switch; an output resonant circuit including the reactive load; and a coupling reactance coupled in series between the RF output current of the driver circuit and an input of the output resonant circuit, the coupling reactance performing a series to parallel impedance match from the driver circuit to the output resonant circuit, the coupling reactance including a first reactance coupled in series between the RF output current of the driver circuit associated with the first switch and an input of the output resonant circuit, and a second reactance coupled in series between the RF output current of the driver circuit associated with the second switch and an input of the output resonant circuit.
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5. A circuit for driving a reactive load with high efficiency comprising:
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a driver circuit for converting DC input current to RF output current, the driver circuit having a differential implementation including a first switch and a second switch; an output resonant circuit including the reactive load and an input for receiving the RF output current; and a coupling reactance electrically connected in series between the driver circuit and the input of the resonant circuit for performing a series to parallel impedance match from the driver circuit to the resonant circuit, the coupling reactance including a first reactance coupled in series between the RF output current of the driver circuit associated with the first switch and an input of the output resonant circuit, and a second reactance coupled in series between the RF output current of the driver circuit associated with the second switch and an input of the output resonant circuit.
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6. In an electronic article surveillance system, an interrogator for monitoring a detection zone by transmitting an interrogation signal into the detection zone and detecting disturbances caused by the presence of a resonant tag within the detection zone, the interrogator comprising:
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a loop antenna for transmitting the interrogation signal; a resonance capacitance connected across the antenna, the antenna and the capacitance forming a resonant circuit; and a driver circuit having an RF output current for driving the resonant circuit, the driver circuit having a differential implementation including a first switch and a second switch, the circuit including a coupling reactance connected in series between the RF output current of the driver circuit and the resonant circuit for performing a series to parallel impedance match from the driver circuit to the resonant circuit, the coupling reactance including a first reactance coupled in series between the RF output current of the driver circuit associated with the first switch and an input of the output resonant circuit, and a second reactance coupled in series between the RF output current of the driver circuit associated with the second switch and an input of the output resonant circuit.
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Specification