Slew rate in low-speed data communication interfaces
A circuit includes an inductive circuit trace and a nonlinear device. The circuit conducts a signal input to a load. The circuit trace receives the signal input at a first end of the circuit trace and provides the signal input to the load at a second end of the circuit trace. The nonlinear device is coupled at the second end and is configured to increase a voltage rise time of the signal input.
1. A circuit for conducting a signal input to a load, the circuit comprising:
an inductive circuit trace to receive the signal input at a first end of the circuit trace, and to provide the signal input to the load at a second end of the circuit trace; and
a nonlinear device coupled at the second end and configured to increase a voltage rise time of the signal input;
wherein:
when the signal input is in a low state, the non-linear element is in a conducting state and drives a current into the circuit trace to a source of the input signal;
when the signal input transitions from the low state to a high state, the non-linear element enters a reverse recovery state that increases the current through the circuit trace, such that a voltage at the load increases at a first rate until a reverse recovery charge on the non-linear element is depleted;
after the reverse recovery charge is depleted, the non-linear element enters an open-circuit state, and the voltage at the load increases at a second rate until an inductive current from the circuit trace is depleted; and
after the inductive current is depleted, the voltage at the load increases at a third rate, wherein the first rate is lower than the third rate and the third rate is lower than the second rate.
2. The circuit of claim 1 , wherein the nonlinear device includes a diode.
3. The circuit of claim 2 , wherein a cathode of the diode is coupled at the second end of the circuit trace.
4. The circuit of claim 3 , wherein an anode of the diode is coupled to a positive voltage source.
5. A method for conducting a signal input to a load, the method comprising:
providing an inductive circuit trace to receive the signal input at a first end of the circuit trace, and to provide the signal input to the load at a second end of the circuit trace; and
providing a nonlinear device coupled at the second end and configured to increase a voltage rise time of the signal input;
wherein:
when the signal input is in a low state, the non-linear element is in a conducting state and drives a current into the circuit trace to a source of the input signal;
when the signal input transitions from the low state to a high state, the non-linear element enters a reverse recovery state that increases the current through the circuit trace, such that a voltage at the load increases at a first rate until a reverse recovery charge on the non-linear element is depleted;
after the reverse recovery charge is depleted, the non-linear element enters an open-circuit state, and the voltage at the load increases at a second rate until an inductive current from the circuit trace is depleted; and
after the inductive current is depleted, the voltage at the load increases at a third rate, wherein the first rate is lower than the third rate and the third rate is lower than the second rate.
6. The method of claim 5 , wherein the nonlinear device includes a diode.
7. The method of claim 6 , wherein a cathode of the diode is coupled at the second end of the circuit trace, and an anode of the diode is coupled to a positive voltage source.
8. A printed circuit board, comprising:
a source device configured to provide a signal input;
an inductive circuit trace to receive the signal input at a first end of the circuit trace;
a load configured to receive the signal input at a second end of the circuit trace; and
a diode device coupled at the second end and configured to increase a voltage rise time of the signal input;
wherein:
when the signal input is in a low state, the diode is in a conducting state and drives a current into the circuit trace to a source of the input signal;
when the signal input transitions from the low state to a high state, the diode enters a reverse recovery state that increases the current through the circuit trace, such that a voltage at the load increases at a first rate until a reverse recovery charge on the non-linear element is depleted;
after the reverse recovery charge is depleted, the diode enters an open-circuit state, and the voltage at the load increases at a second rate until an inductive current from the circuit trace is depleted; and
after the inductive current is depleted, the voltage at the load increases at a third rate, wherein the first rate is lower than the third rate and the third rate is lower than the second rate.