Piecewise linear slew rate control of method for output devices
OwnerJason Gonzalezinventor
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Abstract
A novel method and apparatus is presented for reducing the slew rate signals on transmission lines of integrated circuits. When a transmission line is to be driven to a state by a driver device, the voltage on predrive line controlling the driver device is pulled to a level at or very near to the turn-on threshold voltage the driver device, much more quickly than the turn-on setup time of the driver device. A programmed impedance is then connected between an “on” voltage source and the predrive line to result in a controlled slope of the transmission line signal. Once the voltage level on the transmission line reaches a predetermined reference voltage (e.g., the saturation voltage of the driver device, the predrive line is quickly pulled to the “on” voltage level.
Claims9
A method for reducing the slew rate of a signal on a transmission line driven by an output switching device, said output switching device characterized by a turn-on threshold voltage and comprising a control input responsive to a predrive signal for placing said output switching device in one of an OFF state, a linear state, or an ON state, wherein:
- said output switching device is in said OFF state not driving said transmission line when said predrive signal is at a voltage level between said turn-on threshold voltage and an OFF voltage level;
- said output switching device is in a linear state driving said transmission line to a voltage level proportional to said predrive signal when said predrive signal is at a voltage level between said turn-on threshold voltage and a saturation voltage level;
- and said output switching device is in said ON state driving said transmission line to predetermined constant voltage level when said predrive signal is at a voltage level between said saturation voltage level and said ON voltage level, said method comprising:
- connecting the control input of said output switching device to a voltage source at or near said turn-on threshold voltage;
- connecting a predetermined impedance between an ON voltage source producing said ON voltage level and said control input of said output switching device;
- monitoring a voltage level on at least one of said control input of said output switching device and said transmission line;
- and
- if said monitored voltage level reaches a predetermined reference voltage, connecting said control input of said output switching device to said ON voltage source.
An apparatus for reducing the slew rate of signal on a transmission line of an integrated circuit, comprising:
- an output switching device characterized by an output switching resistance and a turn-on threshold voltage, said output switching device having a control input responsive to a predrive signal for placing said output switching device in one of an OFF state, a linear state, or an ON state, wherein:
- said output switching device is in said OFF state not driving said transmission line when said predrive signal is at a voltage level between said turn-on threshold voltage and an OFF voltage level;
- said output switching device is in a linear state driving said transmission line to a voltage level proportional to said predrive signal when said predrive signal is at a voltage level between said turn-on threshold voltage and a saturation voltage level;
- and said output switching device is in said ON state driving said transmission line to predetermined constant voltage level when said predrive signal is at a voltage level between said saturation voltage level and said ON voltage level;
- a first predrive stage which connects the control input of said output switching device to a voltage source at or near said turn-on threshold voltage;
- a second predrive stage which connects a predetermined impedance between an ON voltage source producing said ON voltage level and said control input of said output switching device;
- a third predrive stage which monitors a voltage level on at least one of said control input of said output switching device and said transmission line;
- and if said monitored voltage level reaches a predetermined reference voltage, connects said control input of said output switching device to said ON voltage source.
Dependencies are inferred from the claim text.