Switchable current source for digital-to-analog converter (DAC)
First Claim
1. A switchable current source comprising:
- a current source having a reference input and a current output;
reference current means coupled to the reference input for supplying a reference current to said current source;
signal generating means for generating an enable signal; and
current switch means coupled to the current output for switching the current output path between an output node and a ground node, said current switch means responsive to the enable signal such that a first current path is provided between the current output and the output node prior to disabling a second current path between the current output and the ground node.
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Accused Products
Abstract
A switchable current source (10) for video DACs that reduces output transients. The switchable current source (10) includes a current mirror (20) connected to a cascode pair (22) for providing a reference current input and a current output. Connected to the reference current input is reference current generator (14) that includes p-channel transistor Q5 for providing a reference current according to the voltage applied at its gate by voltage source (24). A current switch (16) is connected to the current output and includes p-channel transistor Q6 for providing a path to ground and p-channel transistor Q7 for providing a path to an output node. In response to a decoder input DEC, an enable signal generator (18) outputs an enable signal EN and an inverted enable signal ENI to Q7 and Q6, respectively. The enable signal generator (18) includes a delay path (30 and 34) for both the EN and ENI signals so that during a low-to-high transition of signal DEC, EN is delayed so that ENI turns Q7 on before EN shuts off Q6. During a high-to-low transition of DEC, ENI is delayed so that Q6 is turned on before Q7 is turned off.
21 Citations
20 Claims
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1. A switchable current source comprising:
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a current source having a reference input and a current output; reference current means coupled to the reference input for supplying a reference current to said current source; signal generating means for generating an enable signal; and current switch means coupled to the current output for switching the current output path between an output node and a ground node, said current switch means responsive to the enable signal such that a first current path is provided between the current output and the output node prior to disabling a second current path between the current output and the ground node. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. In a current scaling digital-to-analog converter, a current source and switching circuit for providing an output current, comprising:
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at least one current source having a first transistor and a second transistor, the first transistor being gate coupled to both its drain and to the gate of the second transistor, said current source providing a current input transistor and a current output transistor; bias means coupled to the drain of the current input transistor for providing a reference current; enable signal means responsive to an enable input for generating a first enable signal and a second enable signal, said enable signal means including a first delay means for delaying the first enable signal; a first current switch coupled to the drain of the current output transistor, said first current switch responsive to the first enable signal; and a second current switch coupled to the drain of the current output transistor, said second current switch responsive to the second enable signal. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)
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Specification