Gain control scheme independent of process, voltage and temperature
First Claim
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1. An apparatus comprising:
- a driver having at least a pair of transistors disposed in a cascode arrangement having their gate terminals coupled together to receive a bias voltage and their source terminals coupled to receive differential driver current; and
a shunt network coupled across the source terminals of the pair of cascode transistors to operate as a current divider to divert a portion of the differential driver current away from the pair of cascode transistors, in which an amount of current diverted to the shunt network operates to control gain of the driver, and in which the shunt network includes at least one shunt transistor that has its gate terminal coupled to the bias voltage to activate the at least one shunt transistor, the coupling of the gates of the pair of cascode transistors and the gate of the at least one shunt transistor to the same bias voltage cancels circuit variations of the driver that are due to effects of process, voltage and temperature.
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Abstract
An apparatus and method to use a shunt network across source terminals of cascode transistors that drive a differential current to control gain. When the gates of the cascode transistors and transistors of the shunt network are activated by a same bias voltage, the gain control is substantially independent of process, voltage and temperature variations.
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Citations
15 Claims
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1. An apparatus comprising:
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a driver having at least a pair of transistors disposed in a cascode arrangement having their gate terminals coupled together to receive a bias voltage and their source terminals coupled to receive differential driver current; and a shunt network coupled across the source terminals of the pair of cascode transistors to operate as a current divider to divert a portion of the differential driver current away from the pair of cascode transistors, in which an amount of current diverted to the shunt network operates to control gain of the driver, and in which the shunt network includes at least one shunt transistor that has its gate terminal coupled to the bias voltage to activate the at least one shunt transistor, the coupling of the gates of the pair of cascode transistors and the gate of the at least one shunt transistor to the same bias voltage cancels circuit variations of the driver that are due to effects of process, voltage and temperature. - View Dependent Claims (2, 3)
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4. An apparatus comprising:
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a driver having at least a pair of transistors disposed in a cascode arrangement having their gate terminals coupled together to receive a bias voltage, their source terminals coupled to receive differential driver current and their drain terminals coupled to a load; and a gain control network coupled across the source terminals of the pair of cascode transistors to operate as a current divider to divert a portion of the differential driver current away from the pair of cascode transistors, in which an amount of current diverted operates to control gain of the driver, the gain control network includes at least one shunt transistor that has its gate terminal coupled to the bias voltage to activate at least one shunt transistor, the coupling of the gates of the pair of cascode transistors and the gate of the at least one shunt transistor to the same bias voltage cancels circuit variations of the driver that are due to effects of process, voltage and temperature. - View Dependent Claims (5, 6, 7, 8, 9, 10, 11)
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12. A method comprising:
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driving a differential current into source terminals of a pair of transistors disposed in a cascode arrangement and in which a load is coupled to drain terminals of the pair of transistors; providing a bias voltage to gate terminals of the pair of transistors; activating a gain control network coupled across the source terminals of the pair of cascode transistors by selecting one or more transistors from a plurality of shunt transistors to be switched on for activation, in which a gain setting for driving the load is obtained by programmably selecting particular shunt transistor or transistors for activation; providing the bias voltage to activate one or more of the shunt transistors and in which coupling of the gates of the pair of cascode transistors and gates of the shunt transistors that are activated to the same bias voltage cancels circuit variations that are due to effects of process, voltage and temperature; and diverting a portion of the differential current away from the pair of cascode transistors into the gain control network, in which an amount of current diverted operates to control gain of a driver driving the load. - View Dependent Claims (13, 14, 15)
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Specification