Serdes with pin sharing

1. A transceiver comprising:

a first common T-coil circuit coupled to a first input-output pin of the transceiver;

a termination impedance coupled to the first common T-coil circuit and configured to match an impedance of a transmission line coupled to the first common T-coil circuit;

an amplifier configured to receive an input signal from the first input-output pin through the first common T-coil circuit based on a receive enable signal; and

a first transmission buffer configured to transmit an output signal to the first input-output pin through the first common T-coil circuit based on a transmit enable signal,

wherein the first common T-coil circuit comprises:

a first inductor coupled between the transmission line and a center node;

a second inductor coupled between the termination impedance and the center node; and

a third inductor coupled between the first transmission buffer and the center node.

2. The transceiver of claim 1 , wherein the termination impedance comprises:

a variable resistor coupled to the first common T-coil circuit and configured to change resistance according to the receive enable signal or the transmit enable signal; and

a common capacitor coupled to the variable resistor.

3. The transceiver of claim 2 , wherein the variable resistor has a first branch in parallel with a second branch,

wherein the first branch comprises a first resistor coupled in series with a first switch configured to activate in response to a transmit disable signal,

wherein the second branch comprises a second resistor coupled in series with a second switch configured to activate in response to the transmit enable signal, and

wherein the second resistor has a higher resistance than the first resistor.

4. The transceiver of claim 1 , further comprising:

a first receive switch configured to selectively electrically connect or disconnect a center node of the first common T-coil circuit and the amplifier based on the receive enable signal;

a calibration switch coupled to the amplifier and configured to selectively electrically connect or disconnect first and second inputs of the amplifier in response to a calibration enable signal; and

a controller configured to identify an operational mode of the transceiver as a calibration mode, a transmit mode, or a receive mode.

5. The transceiver of claim 4 , wherein the controller is further configured to:

generate a receive disable signal to electrically decouple the amplifier from the first common T-coil circuit;

generate a transmit disable signal to disable the first transmission buffer and to set a variable resistor of the terminal impedance to a first resistance value; and

generate the calibration enable signal to activate the calibration switch.

6. The transceiver of claim 4 , wherein the controller is further configured to:

generate the receive enable signal to electrically couple the amplifier to the first common T-coil circuit to enable the amplifier to receive the input signal from the first input-output pin;

generate a transmit disable signal to disable the first transmission buffer and to set a variable resistor of the terminal impedance to a first resistance value; and

generate a calibration disable signal to deactivate the calibration switch.

7. The transceiver of claim 4 , wherein the controller is further configured to:

generate the receive disable signal to electrically decouple the amplifier from the first common T-coil circuit;

generate the transmit enable signal to enable the first transmission buffer to transmit the output signal to the first input-output pin, and to set a variable resistor of the terminal impedance to a second resistance value; and

generate a calibration disable signal to deactivate the calibration switch.

8. The transceiver of claim 1 , wherein the amplifier is selectively coupled to a center node of the first common T-coil circuit, and

wherein the amplifier comprises a first input and a second input and is configured to amplify a differential signal at the first and second inputs.

9. The transceiver of claim 1 , wherein the amplifier is fixedly coupled to the first common T-coil circuit and the termination impedance, and

wherein the amplifier comprises a first input and a second input and is configured to amplify a differential signal at the first and second inputs.

10. The transceiver of claim 1 , wherein the first transmission buffer comprises a tri-state buffer configured to generate a high-impedance output based on a transmit disable signal.

11. The transceiver of claim 1 , wherein a center node of the first common T-coil circuit is coupled to an electrostatic discharge (ESD) protection diode.

12. The transceiver of claim 1 , further comprising:

a second common T-coil circuit coupled to a second input-output pin of the transceiver; and

a second transmission buffer coupled to the second common T-coil circuit,

wherein the first and second common T-coil circuits are configured to receive a differential input signal at the first and second input-output pins, and

wherein the first and second transmission buffers are configured to output a differential signal to the first and second input-output pins based on the transmit enable signal.

13. The transceiver of claim 12 , further comprising:

a second receive switch configured to selectively electrically connect or disconnect a center node of the second common T-coil circuit and the amplifier based on the receive enable signal.

14. The transceiver of claim 12 , wherein the amplifier is configured amplify a differential signal output from center nodes of the first and second common T-coil circuits.

15. A transceiver comprising:

a pair of common T-coil circuits coupled to a pair of input-output pins of the transceiver;

a termination impedance coupled to the common T-coil circuits and configured to match an impedance of a transmission line coupled to the common T-coil circuits;

an amplifier configured to receive a differential input signal from the input-output pins through the common T-coil circuits based on a receive enable signal; and

a pair of transmission buffers configured to transmit a differential output signal to the input-output pins based on a transmit enable signal,

wherein each of the common T-coil circuits comprises:

a first inductor coupled between the transmission line and a center node;

a second inductor coupled between the termination impedance and the center node; and

a third inductor coupled between a corresponding one of the pair of transmission buffers and the center node.

16. The transceiver of claim 12 ,

wherein the transmission buffers are electrically coupled to corresponding center nodes of the common T-coil circuits.

17. A method of operating a transceiver comprising:

identifying an operational mode of the transceiver as a calibration mode, a transmit mode, or a receive mode; and

in response to identifying the operational mode as the transmit mode:

enabling a transmission buffer to transmit an output signal to an input-output pin of the transceiver through a common T-coil circuit, the input-output pin being coupled to a transmission line;

electrically and physically decoupling an amplifier of the transceiver from the common T-coil circuit by opening a switch that is directly in a signal path between the input-output pin and the amplifier; and

adjusting an impedance of a termination impedance coupled to the common T-coil circuit from a first impedance value to a second impedance value, the first impedance value being matched to an impedance of the transmission line.

18. The method of claim 17 , further comprising:

in response to identifying the operational mode as the receive mode:

electrically coupling the amplifier to the common T-coil circuit to enable the amplifier to receive an input signal from the input-output pin;

disabling first transmission buffer to set a state of the first transmission buffer to a high-impedance state; and

adjusting the impedance of the termination impedance to the first impedance value.

19. The method of claim 17 , further comprising:

in response to identifying the operational mode as the calibration mode:

electrically decoupling the amplifier from the common T-coil circuit;

disabling first transmission buffer to set a state of the first transmission buffer to a high-impedance state; and

activating a calibration switch coupled to the amplifier to electrically couple differential inputs of the amplifier and to enable measurement of an input offset voltage of the amplifier.