DRIVE FOR CASCODE STACK OF POWER FETS
First Claim
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1. A circuit comprising:
- a transistor stack comprising a series connection of a first transistor device, a second transistor device, and an output transistor device, the output transistor device having an output terminal and a control terminal, the first transistor device having an input terminal configured for a connection to a control voltage;
a capacitive coupling between the control terminal and the output terminal configured to drive the control terminal with a coupled signal that continuously tracks an output signal on the output terminal; and
a biasing circuit connected to the control terminal of the output transistor device, the biasing circuit configured to provide a DC bias voltage that is combined with the coupled signal to provide a drive signal on the control terminal, the biasing circuit further configured to respond to changes in a voltage level of the drive signal substantially with no delay in order to maintain a voltage level of the DC bias voltage between a first voltage level and a second voltage level.
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Abstract
Disclosed is a cascode configuration that moves the gate of the cascode substantially without delay relative to an output node by capacitively coupling the latter onto the cascode gates. The passive coupling eliminates the need for actively driving the gates of the cascode. In some embodiments, the only circuitry needed on the cascode gate may be a biasing circuit that limits the swing on the cascode gate between Vmax and 2×Vmax, where Vmax is a transistor device rating.
4 Citations
20 Claims
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1. A circuit comprising:
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a transistor stack comprising a series connection of a first transistor device, a second transistor device, and an output transistor device, the output transistor device having an output terminal and a control terminal, the first transistor device having an input terminal configured for a connection to a control voltage; a capacitive coupling between the control terminal and the output terminal configured to drive the control terminal with a coupled signal that continuously tracks an output signal on the output terminal; and a biasing circuit connected to the control terminal of the output transistor device, the biasing circuit configured to provide a DC bias voltage that is combined with the coupled signal to provide a drive signal on the control terminal, the biasing circuit further configured to respond to changes in a voltage level of the drive signal substantially with no delay in order to maintain a voltage level of the DC bias voltage between a first voltage level and a second voltage level. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A circuit comprising:
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a first stack comprising a first transistor, a second transistor, and a third transistor, the third transistor comprising a control terminal and an output terminal; a second stack connected to the first stack at a node; a biasing circuit connected to the control terminal of the third transistor; and a capacitive coupling between the control terminal of the third transistor and the output terminal of the third transistor configured to couple an output signal at the output terminal as a coupled signal to the control terminal, the biasing circuit configured to provide a DC bias voltage that combines with the coupled signal to produce a drive signal on the control terminal, the biasing circuit further configured to respond to changes in a voltage level of the drive signal with substantially no delay and maintain a voltage level of the DC bias voltage between a first voltage level and a second voltage level as the voltage level of the drive signal changes. - View Dependent Claims (9, 10, 11, 12)
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13. A method in a transistor comprising:
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providing a divided output signal at an output terminal of the transistor as a coupled signal to a control terminal of the transistor using a capacitive coupling between the output terminal and the control terminal; generating a DC bias voltage; providing a drive signal on the control terminal of the transistor by combining the DC bias voltage with the coupled signal; and responding, substantially without delay, to variations in a voltage level of the drive signal by maintaining a voltage level of the DC bias voltage between a first voltage level and a second voltage level, wherein the capacitive coupling comprises a first capacitor connected between the output terminal and the control terminal and a second capacitor connected between a power rail and the control terminal to define a capacitive voltage divider. - View Dependent Claims (14, 15)
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16. (canceled)
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17. A circuit comprising:
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means for providing a divided output signal at an output terminal of a transistor in the circuit as a coupled signal to a control terminal of the transistor using a capacitive coupling between the output terminal and the control terminal; means for generating a DC bias voltage; means for providing a drive signal on the control terminal of the transistor by combining the DC bias voltage with the coupled signal; and means for responding, substantially without delay, to variations in a voltage level of the drive signal to maintain a voltage level of the DC bias voltage between a first voltage level and a second voltage level, wherein the capacitive coupling comprises a first capacitor connected between the output terminal and the control terminal and a second capacitor connected between a power rail and the control terminal to define a capacitive voltage divider. - View Dependent Claims (18, 19)
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20. (canceled)
Specification