Patent ID: 6873196
Filing Date: 2005-03-29
Classification: H03K

Abstract:
1. A method for reducing the slew rate of transition edges of a digital signal on an output pad of an integrated circuit, comprising: connecting a first switchably conductive device characterized by a first threshold voltage of a given polarity between said output pad of said integrated circuit and a voltage source, said first switchably conductive device having a control input connected to a first input signal to allow current conduction from said voltage source to said output pad of said integrated circuit when a voltage level of said first input signal is equal to and greater than said first threshold voltage and to disallow said current conduction when said voltage level of said first input signal is less than said first threshold voltage; connecting a second switchably conductive device independent from said first switchably conductive device and characterized by a second threshold voltage of said given polarity greater than said first threshold voltage between said output pad of said integrated circuit and said voltage source, said second switchably conductive device having a control input connected to a second input signal to allow current conduction from said voltage source to said output pad of said integrated circuit when a voltage level of said second input signal is equal to and greater than said second threshold voltage and to disallow said current conduction when said voltage level of said second input signal is less than said second threshold voltage; connecting between said output pad of said integrated circuit and said voltage source one or more additional independent switchably conductive devices each characterized by a respective threshold voltage of said given polarity but different than said first threshold voltage, said second threshold voltage, and each other respective threshold voltage, each said one or more additional switchably conductive devices having a respective control input connected to a respective input signal to allow current conduction from said voltage source to said output pad of said integrated circuit when a voltage level of said respective input signal is equal to and greater than said respective threshold voltage and to disallow said current conduction when said voltage level of said respective input signal is less than said respective threshold voltage; and connecting a driving signal as said first input signal of said first switchably conductive device and as said second input signal of said second switchably conductive device and as said respective input signal of said respective switch of each of said respective one or more additional switchably conductive devices; wherein said first switchably conductive device, said second switchably conductive device, and said respective one or more additional independent switchably conductive devices together operate to control the slew rate of said output signal driven onto said output pad of said integrated circuit using a step-controlled edge transition.