Matched current source serial bus driver
AssigneeNCR Corporation
InventorsAlexander J. Neudeck, Ernest W. Cordan, Jr.
Life of this patent
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Abstract
A matched current source bus driver circuit providing time and magnitude matched currents as sources and sinks to a pair of serial bus lines. A reference current path is established in transistors which are structurally mirrored to the devices sourcing and sinking bus line currents. Time regulated switching of the reference current ensures RF suppression while maintaining the match of the source and sink current sources driving the bus. Selective decoupling during a loss of circuit ground condition eliminates spurious injection of current into either bus line.
Claims12
A CMOS integrated circuit bus driving transmitter, comprising:
- a first current path between high and low supply voltages including a serial connection of a p-channel reference transistor and a n-channel reference transistor;
- a first current source connected to conduct between the high supply voltage and a high line of the bus in matched response to a control signal shared with the p-channel reference transistor;
- a second current source connected to conduct between the low supply voltage and a low line of the bus, complementary to the high line of the bus, in matched response to a control signal shared with the n-channel reference transistor;
- and
- means for selectively enabling current flow in the first path at a controlled rate of change.
Dependencies are inferred from the claim text.