International Business Machines Corporation

David LeRoy Guertin

Robert Russell Williams

Daniel Mark Dreps

John Michael Borkenhagen

Moises Cases

Nam Huu Pham

Charles Luther Johnson

Daniel Guy Young

Bruce George Rudolph

Dennis T Cox

Joseph James Cahill

Mark E Turner

A method and system for reducing a reflection coefficient below a predetermined value thereby reducing jitter by the variation of the effective impedance of a driver appearing to be bounded during state transitions. The driver may include a pull-up driver and a pull-down driver. In the pull-up driver, the transistors may be switched from a first state to a second state in a staggered fashion where the first state is complementary to the second state; In the pull-down driver, the transistors may be switched from a second state to a first state in a staggered fashion. By staggering the switching of the transistors in the pull-up driver and the pull-down driver, a portion of the current may flow from the pull-up driver to the pull-down driver thereby causing the variation of the effective impedance of the driver to appear to be bounded during state transitions.

Dynamically producing an effective impedance of an output driver with a bounded variation during transitions thereby reducing jitter

A mixed voltage output driver includes an output sensing circuit that senses an output voltage at an output terminal and generates a voltage signal that corresponds to a voltage level at the output terminal. Next, an impedance selection circuit receives the voltage signal and generates a control signal in response to the output voltage having a higher logical uplevel than the mixed voltage output driver. The control signal is then received by an adjustable drive impedance circuit that is also coupled to an input terminal of the mixed voltage output driver and, in response thereto, the adjustable drive impedance circuit modifies an output drive impedance of the mixed voltage output driver. In another advantageous embodiment, the mixed voltage output driver only determines if the output voltage at the output terminal is at a logical uplevel before adjusting the output drive impedance.

Mixed voltage output driver with automatic impedance adjustment

A performance-sensing element (PSE) circuit detects the actual speed of other circuits on the same chip by launching a pulse into a tapped cascade of circuits on the chip, then detecting how far the pulse has progressed after a known interval. Control signals indicating circuit speed can stabilize parameters of the other circuits, such as rate of change of current (di/dt) in driver circuits, absolute delay of clock signals from one chip to another, and relative delay of multiple clock signals within the chip.

VLSI performance compensation for off-chip drivers and clock generation

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Rochester, MN, United States of America

David LeRoy Guertin