Dynamically boosted current source circuit

A dynamically boosted current source circuit for increasing the speed with which a signal from an open drain or open collector transmitting device is pulled down to a known voltage, comprising:

• an input node having an associated capacitance and connected to receive an input signal from an open drain or open collector transmitting device,
• a threshold detector arranged to detect when said input signal has crossed a first predetermined threshold voltage, and
• a current source arranged to provide a first current to said input node when said input signal is above said first predetermined threshold voltage and to provide a boosted current greater than said first current to said input node to pull said input signal down to a known voltage when said input signal falls below said first predetermined threshold voltage, said current source arranged such that the rate at which its output current is slewed from said first current to said boosted current and the amplitude of said boosted current are independent of the slew rate and amplitude of said input signal prior to said current boost, said boosted current increasing the speed with which said associated capacitance is discharged and thereby increasing the speed with which said input node is pulled down to said known voltage.

A dynamically boosted current source circuit for increasing the speed with which a signal from an open drain or open collector transmitting device is pulled up to a known voltage, comprising:

• an input node having an associated capacitance and connected to receive an input signal from an open drain or open collector transmitting device,
• a threshold detector arranged to detect when said input signal has crossed a first predetermined threshold voltage, and
• a current source arranged to provide a first current to said input node when said input signal is below said first predetermined threshold voltage and to provide a boosted current greater than said first current to said input node to pull said input signal up to a known voltage when said input signal exceeds said first predetermined threshold voltage, said current source arranged such that the rate at which its output current is slewed from said first current to said boosted current and the amplitude of said boosted current are independent of the slew rate and amplitude of said input signal prior to said current boost, said boosted current increasing the speed with which said associated capacitance is charged and thereby increasing the speed with which said input node is pulled up to said known voltage.

A method of improving the response speed of a circuit which has at least one capacitive node and is responsive to a transitioning input signal, comprising the steps of:

• providing a first current to at least one capacitive node in a circuit responsive to a transitioning input signal, the speed with which said capacitive node changes state affecting the speed with which said circuit responds to an input signal transition,
• detecting when said input signal is transitioning,
• boosting the current to said at least one capacitive node when an input signal transition is detected to increase the speed with which said capacitive node changes state, said current to said at least one capacitive node boosted at a predetermined rate and to a predetermined amplitude, said predetermined rate and predetermined amplitude independent of the slew rate and amplitude of said input signal.