Partial isolation of power rails for output buffer circuits

An output buffer circuit for delivering output signals of high and low potential levels at an output in response to data signals at an input, said output buffer circuit comprising an input stage coupled between a relatively quiet power supply rail and a relatively quiet power ground rail, and an output stage coupled between a relatively noisy power supply rail and a relatively noisy power ground rail, the improvement for reducing droop in the relatively noisy supply rail for reducing output step in voltage during transition from low to high potential level at the output comprising:

• a first coupling resistor coupled between the relatively quiet and noisy supply rails, said resistor having a low resistance value selected for partially coupling said supply rails while maintaining partial isolation for maintaining input dynamic threshold levels of other non-switching quiet output buffer circuits coupled to a common bus.

A power rail coupling for an output buffer circuit having an output coupled to a common bus with other output buffer circuits, said output buffer circuit having relatively quiet and relatively noisy power ground rails coupled respectively to input and output stages of the output buffer circuit comprising:

• a coupling resistor coupled between the relatively quiet and noisy power ground rails and having a low resistance value selected for partially coupling said ground rails to reduce ground bounce on the noisy power ground rail thereby reducing output step in voltage during high to low transition at the output, said coupling resistor partially isolating said relatively quiet and noisy ground rails to maintain input dynamic threshold levels for other non-switching quiet output buffer circuits coupled to the common bus.

An output buffer circuit for delivering output signals of high and low potential levels at an output in response to data signals at an input, said output buffer circuit comprising an input stage coupled between a relatively quiet power supply rail and a relatively quiet power ground rail, and an output stage coupled between a relatively noisy power supply rail and a relatively noisy power ground rail, the improvement for reducing droop in the relatively noisy supply rail for reducing output step in voltage during transition from low to high potential level at the output comprising:

• a coupling resistor coupled between the relatively quiet and noisy ground rails, said coupling resistor having a low resistance value selected for partially coupling said ground rails to reduce ground bounce and thereby reduce output step in voltage during high to low transitions at the output, said coupling resistor partially isolating the relatively quiet and noisy ground rails for maintaining input dynamic threshold levels for other non-switching quiet output buffer circuits coupled to a common bus.