Methods and apparatus for an interface

1. An interface circuit configured to receive a supply voltage, comprising:

a pair of input pads, comprising a first input pad and a second input pad;

a first input termination resistor connected to the first input pad;

a second input termination resistor connected to the second input pad;

a pair of output pads;

a redriver circuit connected between the pair of input pads and the pair of output pads;

a signal detection circuit connected to the pair of input pads and configured to:

generate a control signal according to a first voltage at the first input pad and a second voltage at the second input pad;

control an operation of the redriver according to the control signal; and

control biasing of the first and second input termination resistors according to the control signal.

2. The interface circuit according to claim 1 , wherein the signal detection circuit comprises a conversion circuit configured to convert the first voltage and the second voltage to a DC voltage.

3. The interface circuit according to claim 2 , wherein the signal detection circuit further comprises a comparator comprising a first input terminal and a second input terminal, wherein the comparator is configured to receive the DC voltage at the first input terminal and a reference voltage at the second terminal.

4. The interface circuit according to claim 3 , wherein the comparator generates the control signal according to the DC voltage and the reference voltage.

5. The interface circuit according to claim 1 , further comprising an internal regulator connected to the first and second input termination resistors and configured to:

generate a regulator voltage; and

provide a first bias to the first and second input termination resistors.

6. The interface circuit according to claim 5 , wherein the interface circuit comprises a selector circuit connected between the internal regulator and the supply voltage and configured to selectively connect the regulator voltage and the supply voltage to the first and second input termination resistors according to the control signal.

7. The interface circuit according to claim 6 , further comprising a control circuit configured to receive the control signal and transmit the control signal to the redriver after a time delay.

8. The interface circuit according to claim 7 , wherein the time delay corresponds to a settling time at the pair of input pads from the supply voltage to the regulator voltage.

9. The interface circuit according to claim 7 , further comprising a timing circuit connected to the control circuit and configured to generate a count value, wherein the control circuit is responsive to the timing circuit.

10. The interface circuit according to claim 1 , wherein the supply voltage provides a second bias to the first and second input termination resistors.

11. A method for operating an interface circuit having a first input termination resistor and a second input termination resistor, comprising:

operating the interface circuit in a first mode comprising biasing the first and second input termination resistors with a supply voltage;

detecting a redriver while the first and second input termination resistors are biased with the supply voltage;

applying an input signal to the redriver;

operating the interface circuit in a second mode comprising switching biasing of the first and second input termination resistors from the supply voltage to a regulator voltage; and

enabling operation of the redriver after biasing the first and second input termination resistors with the regulator voltage.

12. The method according to claim 11 , wherein switching biasing of the first and second input termination resistors from the supply voltage to the regulator voltage comprises:

generating a control signal according to a difference voltage between the first and second input termination resistors; and

transmitting the control signal to a selector circuit.

13. The method according to claim 12 , wherein enabling operation of the redriver comprises transmitting the control signal to the redriver after a time delay.

14. The method according to claim 11 , wherein:

the first mode is a slumber mode; and

the second mode is an active mode.

15. A system, comprising:

a host device connected to a sink device via an interface circuit, wherein the interface circuit comprises:

a redriver circuit connected between a pair of input pads and a pair of output pads;

a pair of input termination resistors connected to the pair of input pads;

a regulator configured to:

generate a regulator voltage; and

bias the pair of input termination resistors with the regulator voltage;

a selector circuit connected to the pair of input termination resistors and configured to bias the pair of input termination resistors with one of the regulator voltage and a supply voltage according to a control signal;

a signal detection circuit connected to the pair of input pads and comprising:

a conversion circuit configured to generate a DC voltage based on a first voltage and a second voltage at the pair of input pads;

a comparator configured to:

receive the DC voltage and a reference voltage;

generate the control signal according to the DC voltage and the reference voltage; and

transmit the control signal to the selector circuit;

a control circuit connected to the signal detection circuit and configured to receive the control signal and transmit the control signal to the redriver after a time delay.

16. The system according to claim 15 , wherein the time delay corresponds to at least one of:

a settling time at the pair of input pads from the supply voltage to the regulator voltage; and

a predetermined compliance specification of the system.

17. The system according to claim 15 , wherein the selector circuit comprises:

a first transistor connected to:

an output of the signal detection circuit at a first terminal; and

the regulator at a second terminal.

18. The system according to claim 15 , wherein the selector circuit comprises:

an inverter connected to the signal detection circuit and configured to receive the control signal; and

a second transistor connected to:

an output of the inverter at a first terminal; and

the supply voltage at a second terminal.

19. The system according to claim 15 , wherein the redriver is configured as a uni-directional redriver.

20. The system according to claim 15 , further comprising a timing circuit configured to generate a count value, wherein the control circuit is responsive to the count value and the time delay corresponds to the count value.