Power amplifier with bootstrap voltage clamp
First Claim
1. An amplifier output stage having an output transistor connected to a high supply voltage and having a bootstrap terminal coupled to a control terminal of the output transistor through control means, the output stage comprising:
- a capacitor arranged between the bootstrap terminal and an output of the output stage for elevating a voltage at the bootstrap terminal above the high supply voltage; and
means for limiting the voltage at the bootstrap terminal to no greater than a predetermined maximum threshold;
wherein the means for limiting directly acts on the control terminal of the output transistor to reduce a conductivity of the output transistor when the voltage at the bootstrap terminal exceeds the predetermined threshold.
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Accused Products
Abstract
An amplifier output stage having an output transistor connected to a high supply voltage and a bootstrap terminal coupled to a control terminal of the output transistor through control circuitry. The output stage includes a capacitor arranged between the bootstrap terminal and the output terminal of the output stage for elevating the voltage at the bootstrap terminal above the high supply voltage, and circuitry for limiting the voltage at the bootstrap terminal to a predetermined threshold. The circuitry for limiting the voltage at the bootstrap terminal directly acts on the control terminal of the output transistor to reduce the conductivity of the output transistor when the voltage at the bootstrap terminal exceeds the predetermined threshold.
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Citations
15 Claims
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1. An amplifier output stage having an output transistor connected to a high supply voltage and having a bootstrap terminal coupled to a control terminal of the output transistor through control means, the output stage comprising:
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a capacitor arranged between the bootstrap terminal and an output of the output stage for elevating a voltage at the bootstrap terminal above the high supply voltage; and means for limiting the voltage at the bootstrap terminal to no greater than a predetermined maximum threshold; wherein the means for limiting directly acts on the control terminal of the output transistor to reduce a conductivity of the output transistor when the voltage at the bootstrap terminal exceeds the predetermined threshold. - View Dependent Claims (2, 3)
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4. A voltage limiting circuit comprising:
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a first terminal to receive a first voltage; a second terminal to receive a second voltage; a voltage divider coupled between the first terminal and a voltage supply terminal, the voltage divider having an output; and a switch having first, second, and third terminals, the first terminal of the switch being coupled to the second terminal of the circuit, the second terminal of the switch being coupled to the output of the voltage divider, and the third terminal of the switch being coupled to a predetermined reference voltage, the switch comparing the output of the voltage divider to the predetermined reference voltage to limit the second voltage to no greater than a predetermined maximum threshold. - View Dependent Claims (5, 6, 7, 8, 9)
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10. A control circuit for controlling a voltage applied to a control terminal of an output transistor, the control terminal of the output transistor being coupled to a bootstrap terminal to receive a bootstrap voltage, the control circuit comprising:
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voltage sensing means, connected to the bootstrap terminal, for sensing a value of the bootstrap voltage; and voltage limiting means, connected to the control terminal of the output transistor and responsive to the voltage sensing means, for limiting the voltage applied to the control terminal to no greater than a predetermined maximum value. - View Dependent Claims (11, 12, 13, 14, 15)
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Specification