Dynamic termination-impedance control for bidirectional I/O pins

• Main Authors: NGUYEN KHAI Q, WANG XIAOBAO, SUNG CHIAKANG, WANG BONNIE I
• Format: Patent
• Language: English
• Published: 07.10.2014
• Subjects: BASIC ELECTRONIC CIRCUITRY; ELECTRICITY; PULSE TECHNIQUE

Circuits, methods, and apparatus for dynamic control of source and termination impedances. One output stage provides a series termination when transmitting and a parallel termination when receiving data. A pull-up device has a nominal impedance of 50 ohms when the output stage pulls a pin from a low voltage to a high voltage, while a pull-down device has a nominal impedance of 50 ohms when the pin is pulled from a high voltage to a low voltage. Both the pull-up and pull-down devices are turned on when receiving data. Due to their non-linear current-voltage characteristics, the pull-up device appears as 50 ohms when the pin voltage is higher than one half the supply voltage, while the pull-down device appears as 50 ohms when the pin voltage is lower than one half the supply voltage. The pull-up and pull-down devices can be calibrated to provide a nominal 50 ohm impedance.